If an insect, a spider, a scorpion, a centipede, or a lobster be examined, the body will be found to be composed of a series of more or less similar rings or segments joined together; and some of these segments will be found to bear jointed legs (Fig. 1). All the animals possessing these characteristics are classed together as the Branch Arthropoda.

A similar segmented form of the body is found among worms; but these are distinguished from the Arthropods by the absence of legs. It should be remembered that many animals commonly called worms, as the tomato-worm, apple-worm, etc., are not true worms, but are the larvae of insects (Fig. 2). The angle-worm is the most familiar example of a true worm.

The Branch Arthropoda is the largest of the branches of the Animal Kingdom, including many more known species than all the other branches taken together. Our common representatives are distributed among four classes: these are the Crustacea, the Arachnida, the Myriapoda, and the Hexapoda. The first three classes are briefly discussed in this chapter; the fourth comprises the Insects, and is the subject of the remaining parts of this book.

The following table will enable the student to distinguish the classes of the Arthropoda.*

* The following is the method of using the analytical tables given in this book: Read carefully the statement of characteristics given opposite A and AA respectively, and by examining the animal to be classified determine which is true of this animal. This will indicate in which division of the table the name of the group to which the animal belongs is to be looked for. If this division of the table is subdivided, pass to B and BB (also to BBB if it occurs) in this division and determine in a like manner under which the animal belongs. Continue in this way, passing to the letters C, D, E, etc., in regular order till the name of the group is reached. Then turn to the page indicated and read the description or the group given there, comparing the specimens with the description. It should be borne in mind that an analytical table is merely an aid to the determination of groups. As the groups that we recognize are not always sharply limited in nature, we cannot expect to be able in every case to find characters that will serve to distinctly separate them in a table. Therefore when a student has determined by the aid of a key to what group a species seems to belong, he should verify this determination by a study of the characters of that group given in the detailed discussion of it.
 
 

The members of this class are aquatic Arthropda, which breathe by true gills. They have two pairs of antennae and at least five pairs of legs.

The most familiar illustrations of the Crustacea are the Cray-fishes, the Lobsters, the Shrimps, and the Crabs. Cray-fishes (Fig. 3) abound in our brooks, and are often improperly called Crabs. The Lobsters, the Shrimps, and the true Crabs live in salt water.

The Crustaceans are distinguished from all other Arthropods by their mode of respiration, being the only ones that breathe by true gills. Many insects live in water, and are furnished with gill:like organs; but these are tracheal gills, organs which differ essentially in structure from true gills, as described later, in the chapter on Anatomy of Insects. The Crustacea also differ from other Arthropoda in having two pairs of antennae; and from all except the Myriapoda in having many (more than four) pairs of legs.

The illustrations named above are the more conspicuous members of the class; but many other smaller forms abound both in the sea and in fresh water. Some of the more minute fresh-water forms are almost sure to occur in any fresh water aquarium. In Figure 4 are represented three of these, greatly enlarged.

Among the Crustacea that live in damp places on land the Sow-bugs, Oniscidae (O-nis'ci-dae), are most often seen. These frequently occur about water-soaked wood; and are often mistaken, by students beginning the study of Entomology, for insects or Myriapods. Figure 5 represents a Sow-bug.

On the sea-coast an immense number of forms of Crustacea occur.
 

The members of this class are air-breathing Arthropods, in which the head and thorax are grown together, forming a cephalothorax, which have four pairs of legs fitted for walking, and which have no antennae.

The Arachnida abound wherever insects occur, and are often mistaken for insects. But they can be easily distinguished by the characters given above, even in those cases where an exception occurs to some one of them. The more important of the exceptions are the following: In the Sol-pugida the head is distinct from the thorax; as a rule the young of mites have only six legs, but a fourth pair are added during growth; and in the gall mites (Phytoptus) there are only four legs.

In the Arachnida we find only simple eyes.

The cephalothorax (ceph-a-lo-tho'rax) bears six pairs of appendages--two pairs of jaws, and four pairs of legs. The first pair of jaws are the mandibles (man'di-bles), the second, the maxillae (max-il'lae).

The mandibles (Fig. 6, md) lie in front of and above the mouth, and consist each of two or three segments. They serve for seizing prey, and often also for killing it. In many books they are termed the chelicerae (che-lic'e-rae).

The maxillae (Fig, 6, mx) lie just behind the mandibles, one on each side of the mouth. Each maxilla bears a large feeler or palpus (Fig. 6, p). These palpi vary greatly in form; frequently they resemble legs; hence many Arachnida appear to have five pairs of legs. The palpi are often so largely developed that each maxilla appears to be merely the first segment of its leg-like palpus. These appendages are often called the pedipalpi (ped-i-pal'pi). But as the name Pedipalpi is applied to one of the orders of the Arachnida, we will call these appendages the palpi.

The legs of Arachnida consist typically of seven parts (Fig. 7), which are named, beginning with the one next to the body, as follows: 1, coxa (cox'a); 2, trochanter (tro-chan'- ter); 3, femur (fe'mur); 4, patella (pa-tel'la); 5, tibia (tib'i-a); 6, metatarsus (met-a-tar'sus); and 7, tarsus (tarsus). The tarsus may be composed of several segments, and is usually furnished with claws.

Two forms of breathing organs are found in this class: one, tracheae, resembling the tracheae of insects, described in the chapter on the anatomy of insects; and the other, tracheal lungs or lung sacs, which consist of many leaf-like plates enclosed in a sac. Both forms open by paired spiracles, which are usually situated on the lower side of some of the abdominal segments.

Very great differences exist in the several orders of the Arachnida in respect to the division of the body into segments. In arranging the orders in a series, we place first those in which the segments of the body are most distinctly indicated, while those which seem to depart more widely from the segmented type characteristic of the Arthropoda are placed later.

The class Arachnida includes seven orders; these are designated as follows:

The Scorpions	Order SCORPIONIDA (p. 15)
The Jointed Spiders	Order SOLPUGIDA (p. I6)
The Pseudoscorpions	Order PSEUDOSCORPIONES (p. 17)
The Whip-scorpions	Order PEDIPALPI (p. I7)
The Harvestmen	Order PHALANGIDEA (p. 19)
The Spiders	Order ARANEIDA (p. 20)
The Mites	Order ACARINA (p. 42)

With the scorpions (Fig. 8), the body is divided into a compact, unsegmented cephalothorax, and a long, segmented abdomen.  The abdomen is divided into two portions: a broad pre-abdomen, consisting of seven segments; and a slenderer tail-like division, the post-abdomen, consisting of five segments.  At the end of the post-abdomen there is a large poison-sting, which appears like a segment. The mandibles and the palpi are provided with pincers.  As the palpi are very large, with stout pincers, they resemble in a striking manner the great claws of lobsters.  The cephalothorax bears from three to six pairs of eyes. Scorpions breathe by means of lung sacs, of which there are four pairs, opening on the lower side of the third to the sixth abdominal segments.

Full-grown scorpions possess a pair of comb-like organs on the lower side of the second abdominal segment.  The function of these organs is not yet known.

The sexes of scorpions differ in that the male has broader pincers and a longer post-abdomen. Scorpions do not lay eggs, the young being developed within the mother.  After the birth of the young, the mother apparently shows great regard for them, carrying them about with her for some time, attached by their pincers to all portions of her body.

Scorpions live in warm countries.  They are common in the southern portion of the United States, but are not found in the North.  They are nocturnal, remaining concealed during the day, but leaving their hiding-places at dusk.  When they run the post-abdomen is bent upwards over the back.  They feed upon spiders and large insects, which they seize with the large pincers of their palpi, and sting to death with their caudal poison sting.

The sting of a scorpion rarely if ever proves fatal to man, although the larger species, which occur in the Tropics, produce serious wounds.

Nearly twenty species are known from North America.
 

The members of this order differ from all other Arachnida in having the head separate from the thorax, and in having the thorax composed of three distinct segments, as with insects. The mandibles are very large, and are furnished with strong pincers. The palpi are shaped like the legs, and are said to be used in locomotion. The first of the four pairs of true legs, like the palpi, are not furnished with claws, and are used as palpi. There are only two eyes. Respiration is effected by means of tracheae, which open through three pairs of spiracles, situated in the first thoracic and the second and third abdominal segments.

Only a few species of Solpugida occur in the United States, and specimens of these are rarely found. So far as is known, our species are nocturnal, remaining concealed during the day. They prey upon small insects, and are believed to be harmless. Figure 9 will serve to show the appearance of these curious animals. The popular name, jointed-spiders, is suggested by the segmented condition of the abdomen.
 

The pseudoscorpions (Fig. 10) are small Arachnida, which resemble scorpions in the form of their body, except that the hinder part of the abdomen is not narrow, as is the post-abdomen of scorpions, and they have no caudal poison-sting. The abdomen is broad, flat, and composed of eleven segments, or in some cases of only ten.

The pseudoscorpions possess only one or two pairs of eyes, and in some, eyes are wanting. They breathe by means of trachea, which open through two pairs of spiracles on the lower side of the second and third abdominal segments.

These little scorpion-like creatures live under stones, beneath the bark of trees, in moss, and in the dwellings of man, between the leaves of books, etc. They run rapidly, sidewise and backwards; and feed on mites and small insects. They are often found attached to insects, especially to flies; but they probably do not feed on these large insects, but merely use them as means of rapid locomotion.

The pseudoscorpions occur in the Northern States as well in the South.
 

These strange creatures are found only in the extreme southern part of our country, being tropical animals. In their general form they have some resemblance to scorpions. They can be easily distinguished by the form of the front legs, which are greatly elongated, and have the tarsi broken up into many small segments; this gives these legs a more or less whip-lash-like appearance. In one family the abdomen also bears a whiplash-like appendage.

The mandibles are furnished with claws; the palpi are very large and armed with strong spines, and the abdomen is distinctly separated from the thorax. The order includes two families, both of which are represented in the United States.
 

This family is represented in the United States by only a single species, the Giant Whip-scorpion, Thelyphonus giganteus (The-lyph'o-nus gi-gan-te'us). This species measures when full grown from four to five inches in length.  Figure 11 represents one less than natural size. These whip-scorpions are greatly feared on account of their supposed venomous powers, but it is probable that there is no foundation for this fear. Although it has been stated often that their bites are poisonous, we can find no direct evidence that it is so. They destroy their prey by crushing it with their palpi.
 

This family is represented in our fauna by the genus Phrynus (Phry'nus), the members of which are smaller than the Giant Whip-scorpion. In this family the front legs are even more whip-lash-like than in the preceding family; the whole body is relatively shorter and broader; the abdomen is joined to the thorax by a slender stalk, and the tail-like appendage is lacking.
 

The Harvestmen are very common in most parts of the United States.  They are well known to children in this country under the name Daddy Long Legs, but as this name is also sometimes applied to Crane-flies, Harvestmen is preferable. In some sections of the country the Har-vestmen are known as Grandfather Graybeards.

Most Harvestmen can be recognized by their very long and slender legs (Fig. 12), although some species have comparatively short ones.  The cephalothorax is indistinctly if at all segmented.  The abdomen is short, broad, consists of six segments, and is without a tail-like appendage; it is broadly joined to the cephalothorax.

The eyes of the Harvestmen are two in number, and are situated on a prominent tubercle near the middle of the cephalothorax. The mandibles are pincer-like.  The maxillae are large, and so opposed as to act as jaws; their palpi are four-jointed, and are small compared with the palpi of the preceding orders; they resemble in form and function the palpi of insects.  The members of this order breathe by tracheae, which open by a single pair of spiracles, on the lower side of the body at the junction of the cephalothorax and abdomen.

The Harvestmen feed on small insects, especially Aphids, and are perfectly harmless.  They are said to devour their prey, chewing it with their maxillae, and swallowing it, instead of merely sucking out the blood, as do most other Arachnida.

Although the Harvestmen have stilt-like legs, they do not raise the body much above the ground when they walk, but carry it quite near their feet, with the middle part of their legs high in the air.  They are said to pounce upon their prey as does a cat upon a mouse, and seize it with their palpi as if with hands.

It is a common practice with children to catch these creatures and say to them, "Grandfather Graybeard, tell me where the cows are, or I'll kill you."  As the poor frightened animal points its legs in all directions in its frantic efforts to escape, it usually earns its freedom; but too often it is not without the loss of one or more legs.

The Spiders differ from other Arachnida in having the abdomen unsegmented and joined to the cephalothorax by a short, narrow stalk.  The cephalothorax is also unsegmented; and the abdomen bears at its end organs for spinning silk (Fig. 13).

The mandibles (Fig. 14, md) consist of two segments, a strong basal one and a claw-shaped terminal one, at the tip of which a poison gland opens (Fig. 15).  It is by means of these organs that spiders kill their prey. The palpi are leg-like in form, but differ greatly according to sex.  In the female the last segment of the palpus resembles a foot of the spider, and is usually armed with a well-developed curved claw. But in the male the corresponding segment is more or less enlarged, and very complicated in structure (Fig. 16).  The greater number of spiders have four pairs of eyes (Fig. 17), but there may be only one, two, or three pairs; and certain cave spiders are blind. Spiders breathe by means of lung-sacs, of which there are one or two pairs; and some have tracheae also. The lung-sacs open on the lower side of the abdomen near its base, and between them is the opening of the reproductive organs. The tracheae open through a single spiracle near the hind end of the body, just in front of the spinning organs.

The spinning organs, which are situated near the end of the abdomen, consist of two or three pairs of spinnerets. These appendages (Fig. 18) are more or less finger-like in form, and sometimes jointed. Upon the end of each spinneret there are many small tubes, the spinning tubes, from which the silk is spun (Fig. 19). Some spiders have as many as one hundred and fifty or two hundred of these spinning-tubes on each spinneret. The silk is in a fluid state while it is within the body, but it hardens as soon as it comes in contact with the air.

Ordinarily the tips of the spinnerets are brought close together, so that all the minute threads that emerge from the numerous spinning tubes unite to form a single thread. This, however, may be so delicate as to be invisible, except in a favorable light. Sometimes a spider will spread its spinnerets apart, and thus spin a broad ribbon-like band. We have observed a spider seize a large grasshopper which was entangled in its web, and, rolling it over two or three times, completely envelop it in a sheet of silk spun from its spread-apart spinnerets.

In the construction of their web some spiders make use of two kinds of silk. One of these is dry and inelastic; the other, viscid and elastic. This fact can be easily seen by examining an orb-web. If the spiral line which forms the greater part of the web be touched, it will adhere to the finger, and will stretch, when the finger is withdrawn, to several times the original length. But if one of the radiating lines or a portion of the outer framework be touched, it will neither adhere to the finger nor be stretched. If the spiral line be examined with a lens, it will be found to bear numerous bead-like masses of viscid matter (Fig. 20); this explains its adhesiveness.

It is supposed that the two kinds of silk are spun from different spinnerets, and that the viscid silk comes from the front pair. When this silk is first spun the viscid matter forms a continuous layer of liquid on the outside of it. But very soon this layer breaks up into the bead-like masses --in a way similar to that in which the moisture on a clothes-line in a foggy day collects into drops.

Spiders of the two families Dictynidae and Uloboridae have spinning organs differing from those of all other spiders. They have in front of the usual spinnerets an additional organ, which is named the cribellum (cri-bel'lum) (Fig. 21). This bears spinning-tubes like the other spinnerets, but these tubes are much finer. These spiders have also on the metatarsus of the hind legs one or two rows of curved spines: this organ is the calamistrum (cal-a-mis'trum) (Fig. 22). By means of the calamistrum these spiders comb from the cribellum a band of loose threads, which form a part of their webs.

Spiders make use of silk in the construction of their webs or snares, in the building of tubes or tents within which they live, in the formation of egg-sacs, and in locomotion.

Fig. 23 represents the large egg-sac of one of the orb-weavers. This is made in the autumn, and contains at that season a large number of eggs five hundred or more. These eggs hatch early in the winter; but no spiders emerge from the egg-sac until the following spring. If egg-sacs of this kind be opened at different times during the winter, as was done by Dr. Wilder, the spiders will be found to increase in size but diminish in number as the season advances. In fact, a strange tragedy goes on within these egg-sacs: the stronger spiders calmly devour their weaker brothers, and in the spring those which survive emerge sufficiently nourished to fight their battles in the outside world.

The egg-sacs of the different species of spiders vary greatly in form. In some, as in that figured above, the outer covering is very dense, while in others the outer part consists of loose flossy silk (Fig. 24). One of the most common kinds is very flat, silvery in color, and is firmly attached to stones lying upon the ground (Fig. 25).

Every one knows that a spider wishing to descend to some place beneath it simply fastens a line to the object which it is upon and then drops boldly off, regulating the rate of its descent by spinning the line rapidly or slowly; when the spider wishes to return, it has only to climb up the same line.

Frequently spiders pass from point to point in a horizontal direction by means of silken bridges. These are formed in this way: The spider spins out a thread, which is carried off by a current in the air. After a time the thread strikes some object and adheres to it; then the spider pulls the line tight, and fastens it where it is standing. It then has a bridge, along which it can easily run.

But more remarkable than either of these uses of silk for locomotion is the fact that many spiders are able to travel long distances, hundreds of miles, through the air by means of these silken threads--
 

The Aeronautic Spiders, or Flying Spiders, as they are more commonly called, are frequently very abundant, especially in warm autumn days. At such times innumerable threads can be seen streaming from fences, from bushes, and the tips of stalks of grass, or floating through the air. The flying spider climbs to some elevated point, which may be merely the tip of a stalk of grass, and then, standing on the tips of its feet, lifts its body as high as it can, and spins out a thread of silk. This thread is carried up and away by a current of air. When the thread is long enough the force of the air current on it is sufficient to buoy the spider up. It then lets go its hold with its feet and sails away. That these spiders travel long distances in this manner has been shown by the fact that they have been seen floating through the air at sea far from land.

Representatives of nearly thirty families of spiders have been found in the United States. But some of these families include only rare species, and others are represented by so few species that we cannot discuss them here. The greater number of our spiders belong to the eleven families described below. The following table will aid the student in separating these families.
 

Those who live in the warmer parts of our country know well the large spiders commonly called Tarantulas. These are the giants among spiders, some of them being the largest known; but some species of this family are not very large. They are dark-colored, hairy spiders, and can be distinguished from the other families mentioned here by the fact that the claw of the mandibles works up and down instead of side wise.

The members of this family do not construct true webs, but they dig long tubes in the earth, which they line with silk, or line their hiding-places in clefts in trees or elsewhere with a layer of silk. They live only in warm countries.

One of the best known of the Tarantulas is Eurypelma hentzii (Eu-ryp'el-ma hentz'i-i). This species occurs in the South and in the Middle West, and is the largest of our spiders (Fig. 26). Several closely allied species are found in California.

But the members of this family that have attracted most admiration on account of their habits are the Trap-door Spiders. These dig a tube in the ground, as do many other members of this family; but this tube is lined with a denser layer of silk, and is provided with a hinged lid, which fits the opening of the tube with wonderful accuracy (Fig. 27).

The spider hides in this nest when not seeking its prey. Some species take the precaution to build a branch to their nest, and to provide this branch with a door. As this door forms a part of one side of the main tube, it is not likely to be observed by any creature which may find its way past the first door of the nest.

Several species of Trap-door Spiders occur in the Southern and Southwestern States.
 

There are certain dark-colored spiders that spin no web, but wander about at night in search of prey, and hide under leaves and stones during the day-time. Many of them make silken tubes, in which they hide in winter or while moulting or laying eggs. Hence they have been .termed Tube Weavers, a name which is also applied to certain other spiders. We will therefore call the members of this family the Drassids (Dras'sids).

In this family the body is long, and is usually flattened above. It is carried near the ground in walking. The legs are rather short and stout; the second pair are not longer than the fourth, and the feet are furnished with only two claws (Fig. 28). The eyes are in two nearly straight rows, and the maxillae are concave or furnished with a furrow (Fig. 29). One of the most common species in the East is Drassus saccatus (Dras'sus sac-ca'tus) (Fig. 30). It lives under stones, in a large bag of silk, in which the female stays with her egg-sac. In early summer a male and female live together in the nest.
 

There may be found during summer, in flat tubular nests on plants, usually in rolled leaves, spiders that spin no webs to entrap their prey.

These spiders very closely resemble the Drassids in structure, but are usually lighter in color, with the legs a little longer and more slender, and the abdomen more nearly cylindrical (Fig. 31). They are also distinguished by the form of the maxillae, which are convex (Fig. 32). These spiders belong to the family Clubionidae. As we have no appropriate common name for these spiders, they may be called the Clubionids (Clu-bi-on'ids).

During the winter the Clubionids hide under bark or stones, and make tubular nests in these places.

Even the most careful observers seldom realize what an immense number of spider-webs are spun upon the grass in the fields. But occasionally these webs are made visible in the early morning by the dew which has condensed upon them: At such times we may see the grass covered by an almost continuous carpet of silk.

The greater number of the webs seen at such times are of the form which we term funnel-webs. They consist of a concave sheet of silk, with a funnel-shaped tube at one side, and numerous lines extending in all directions to the supporting spears of grass (Fig. 33). The tube serves as a hiding-place for the owner of the web; from this retreat the spider runs out on the upper surface of the web to seize any insect that alights upon it. The tubes open below, near the roots of the grass; so that the spider can escape from it if a too formidable insect comes upon the web.

The funnel-web weavers (family Agalenidae) are long-legged, brown spiders, in which the head part of the cephalo-thorax is higher than the thoracic part, and distinctly separated from it by grooves or marks at the sides. The eyes are usually in two rows, but in Agalena the middle eyes of both rows are much higher than the others. The feet have three claws. The posterior pair of spinnerets are two-jointed, and usually longer than the others.

The common grass spider, which abounds in all parts of the United States, is Agalena naevia (Ag-a-le'na nae'vi-a) (Fig. 34).

Certain spiders are remarkable for using two kinds of silk in the formation of their webs. Thus, as explained later, the Orb Weavers build the framework of their orbs of dry and inelastic threads, and attach to this framework a thread which is sticky and elastic; while most spiders which make irregular webs use only one kind of silk. There are, however, certain species of irregular web-weavers which use two kinds of silk. One of these is a plain thread like that spun by other spiders, and the other is a peculiar curled thread or a delicate band of tissue in which there are curled threads.

The curled-thread weavers represent two families, one of which makes irregular webs; the other, those which are of definite form. The first of these is the Dictynidae.

The curled-thread or tissue-like band is made in the same way by both families. It is composed of silk spun from a special spinning-organ, situated in front of the ordinary spinnerets, and named the cribellum (cri-bel'lum); and is combed into its peculiar form by means of a comb of stiff hairs, the calamistrum (cal-a-mis'trum), which is borne by the metatarsus of the hind legs (see page 23). In making the curled thread the spider turns one of its hind legs under the abdomen so that the calamistrum is just under the cribellum, and the foot rests on the other hind leg. It then moves its hind legs back and forth rapidly, so that the calamistrum combs out from the spinning-tubes, and at the same time tangles, a band of fine threads.

This band of tangled or curled threads is easily seen in the webs of these spiders, being wider than the ordinary threads and white in color. In old webs it becomes conspicuous by the large amount of dust which it collects. Figure 35 shows the appearance of this band when magnified, and the way in which it is attached to the plain threads.

Our more common Dictynids make webs of various shapes, on fences, under stones, in holes in rotten logs, and on plants. These webs are especially common among the flowers of Golden-rod and other plants having clusters of small flowers (Fig. 36), and exhibit a slight degree of regularity.
 

Many are the kinds of webs spun by different spiders. Some of them, as the orb-webs and the funnel-webs, delight us with their wonderful regularity of form; while others appear to be a mere shapeless maze of threads. Such are the structures whose presence in the corners of our rooms torment thrifty housewives, and which are disrespectfully termed cobwebs.

The cobweb weavers (Family Theridiidae) are small spiders with unusually slim, legs. The space between the eyes and the front edge of the head is greater than the region occupied by the eyes (Fig. 37); the eyes are in two rows; and the feet are furnished with three claws (Fig. 38), This family includes many species, being in fact the largest of all of the families of spiders. Figure 39 represents a widely distributed species.

Although the house spiders are the most familiar members of this family, the greater number of species spin their webs in the fields on bushes. These webs usually consist of a flat or curved sheet, under which the spider hangs back downward. This sheet is supported by threads running in all directions to the neighboring objects. Frequently there is a large number of these supporting threads above the web, which serve the additional purpose of impeding the flight of insects, and causing them to fall into the web, where they are caught.

Some of these spiders do not remain in their webs, but have a nest in a neighboring crack or corner, from which they rush to seize their prey. And sometimes there is a funnel-shaped tube leading to this nest. But these spiders differ from the true funnel-web weavers in running back downwards on the lower side of their web.

Few if any of the structures built by lower animals are more wonderful than the nets of orb-weaving spiders, but these beautiful objects are so common that they are often considered hardly worthy of notice. If they occurred only in some remote corner of the earth, every one would read of them with interest.

The nets of the different species of orb weavers differ in the details of their structure, but the general plan is quite similar. There is first a framework of supporting lines. The outer part of this framework is irregular, depending upon the position of the objects to which the net is attached; but the more central part is very regular, and consists of a number of lines radiating from the center of the net (Fig. 41). All of these supporting lines are dry and inelastic. But there is spun upon the radiating lines in a very regular manner a thread which is sticky and elastic (Fig. 20, p. 23). Usually this sticky thread is fastened to the radiating lines so as to form a spiral, but a few species make nets in which this thread is looped back and forth.

Many of the orb weavers strengthen their nets by spinning a zigzag ribbon across the center. This ribbon is made by spreading the spinnerets apart so that the minute threads from the spinning tubes do not unite to make a single thread, as is usually the case.

Some of the orb weavers live in their nets hanging head downwards, usually near the center of the net; others have a retreat near one edge of the net, in which they hang back downwards. While resting in these retreats they keep hold of some of the lines leading from the net, so that they can instantly detect any jar caused by an entrapped insect.

When an insect in its flight touches one of the turns of the sticky line, the line sticks to it; but it stretches so as to allow the insect to become entangled in other turns of the line. If it were not for this elasticity of the sticky line, most insects could readily tear themselves away before the spider had time to reach them.

In making its web an orb weaver first spins a number of lines extending irregularly in various directions about the place where its orb is to be. This is the outer supporting framework. Often the first line spun is a bridge between two quite distant points. This is done as described on p.

Having a bridge across the place where the web is to be, it is an easy matter for the spider to stretch its other lines where it wishes them. In doing this it fastens a thread to one point, and then walks along to some other point, spinning the thread as it goes, and holding it clear of the object on which it is walking by means of one of its hind legs. When the second point is reached the thread is pulled tight and fastened in place.

After making the outer framework the radiating lines are formed. A line is stretched across the space so as to pass through tile point which is to be the center of the orb. In doing this the spider may start on one side, and be forced to walk in a very roundabout way on the outer framework to the opposite side. It carefully holds the new line up behind it as it goes along, so that it shall not become entangled with the lines on which it walks; one or both hind feet serve as hands in these spinning operations. The spider then goes to the point where the centre of the orb is to be, and fastening another line there, it walk back to the outer framework, and attaches this line an inch or two from the first. In this way all of the radiating lines are drawn. The next step is to stay these radii by a spiral line which is begun at the center, and attached to each radius as it crosses it. The turns of this spiral are as far apart as the spider can conveniently reach, except at the center of the web. All of the threads spun up to this stage in the construction of the web are dry and inelastic. The spider now proceeds to stretch upon this framework a sticky and elastic line, which is the most important part of the web, the other lines being merely a framework to support it. In spinning the sticky line the spider begins at the outer edge of the orb, and passing around it fastens this line to each radius as it goes. Thus a second spiral is made. The turns of this spiral are placed quite close together, and the first spiral, which is merely a temporary support, is destroyed as the second spiral progresses. Figure 41 represents a web in which the second spiral is made over the outer half of the radii. In this figure, aa represents the temporary stay-line; bb, the sticky spiral; and cc, the fragments of the first spiral hanging from the radii.

Tile orb weavers (Family Epeiridae) are usually plump spiders, the abdomen being large, and often nearly spherical. The space between the eyes and front edge of the head is less than the region occupied by the eyes (Fig. 42).

The eyes are arranged in two rows. The front legs are longer than the others. The feet have three claws (Fig. 43), and the spinnerets are all short. In some species of this family the male is much smaller than the female.

We have already described the thread-curling habits of the Dictynids (p. 32), and the curious organs called cribellum and calamistrum (Fig. 44), by which these curled threads are made (p. 23). Similar organs and a similar habit are possessed by the spiders of the family Uloboridae. These spiders, however, make webs which are regular in form. There are only two genera belonging to this family in the United States; but as the webs made by these are very different, we will describe both.

The Triangle Spider, Hyptiotes cavatus (Hyp-ti'otes ca-va'tus).--This spider is common all over New England and the Middle States, and has been found as far to the southwest as Texas. Its web is most often found stretched between the twigs of a dead branch of pine or spruce. At first sight this web appears like a fragment of an orb web (Fig. 45); but a little study will show that it is complete. The accompanying figure, by Dr. Wilder, who first described the habits of this spider (see Popular Science Monthly, 1875), illustrates the form of the web. It consists of four plain lines corresponding to the radiating lines of an orb web, and a series of double cross lines, which are spun by the cribel-lum and calamistrum. From the point where the radiating lines meet a strong line extends to one of the supporting twigs. Near this twig the spider rests, pulling the web tight so that there is some loose line between its legs, as shown in the enlarged figure. When an insect becomes entangled in one of the cross lines, the spider suddenly lets go the loose line so that the whole web springs forward, and the insect is entangled in other cross threads. The spider then draws the web tight and snaps it again. This may be repeated several times before the spider goes out upon the web after its prey.

Uloborus (U-lob'o-rus).--The spiders of this genus make round webs which resemble at first sight those of the Orb Weavers; but they differ from the ordinary orb webs in that the spiral thread is made of curled or hackled silk. These webs are nearly horizontal, and are usually made between stones or in low bushes. The spiders of this genus are not common, but they are widely distributed. They have not, however, been reported as yet from the Pacific coast.
 

There are certain spiders which are called crab spiders, on account of the short and broad form of the body, and the curious fact that they can walk more readily sidewise or backward than forward.

These spiders spin no webs, but lie in wait for their prey. They live chiefly on plants and fences, and in the winter hide in cracks and under stones and bark. Most of the species are marked with gray and brown, like the bark upon which they live. Some species conceal themselves in flowers, where they lie in wait for their prey. These are brightly colored, like the flowers they inhabit; so that insects visiting flowers may alight within reach of a spider before seeing it.

In this family the legs are turned outward and forward more than downward; so that the body is carried close to the ground. The second pair of legs are as long as or longer than the fourth pair. The eyes are small, nearly equal in size, and arranged in two rows.

One of the best-known members of this family is the female of Misumena vatia (Mi-su'me-na va'ti-a). This is milk-white, with sometimes a light crimson mark on each side of the abdomen, and is found within flowers (Fig. 46).
 

Every collector of insects who has searched for specimens under stones and logs is familiar with the large, dark-colored, hairy spiders often found in these places. These spiders frequently attract especial attention by dragging after them a large gray ball (Fig. 47); this is the egg-sac, which the female carries about with her attached to her spinnerets. These spiders run swiftly; and as they depend on the use of their legs for the capture of their prey, they are well termed Running Spiders.

These spiders resemble in general appearance and in habits the Tarantulas of the South and the West. But none of our species attain the great size of some of the Tarantulas, and in the Running Spiders the claw of the mandibles moves horizontally instead of vertically.

In this family the body is hairy and usually much longer than broad. The eyes differ markedly in size, and are arranged in three or four rows. The larger eyes are not in the front row. The legs are rather long and quite stout.

Like the Tarantulas, some of the Running Spiders build tubular nests in the ground, which they line with silk. Sometimes the entrance to these nests is concealed by small sticks and leaves, and sometimes the spider builds a regular turret over the entrance of its tube (Fig. 48). These nests are used merely as retreats, the spiders wandering forth in search of their prey.

The larger members of our common species belong to the genus Lycosa (Ly-co'sa). These drag after them their egg-sacs as described above; and when the young hatch they climb on their mother's back, and are carried about for a time. The females of the genus Dolomedes (Dol-o-me'des), which also belongs to this family, carry their egg-sac in their mandibles until the young are ready to hatch. At this time the mother fastens the egg-sac in a bush, and spins a web of irregular threads about it, among which the young spiders remain for a time.
 

The Jumping Spiders are of medium size, with a short body and short stout legs (Fig. 49). They are common on plants, logs, fences, and the sides of buildings. They are very apt to attract attention by their peculiar appearance; their short stout legs, bright colors, conspicuous eyes, and quick, jumping movements being very different from those of ordinary spiders.

The eyes are arranged in three or four rows; the front middle pair are the largest, and are very conspicuous. These self-possessed spiders. are able to stare an ordinary observer out of countenance. They move sidewise or backward with great ease, and can jump a long distance. They make no webs except nests in which they hide in winter or when moulting or laying eggs.

In certain members of this family the body is longer than in the typical forms, and ant-like in appearance.

In this order the abdomen is unsegmented and fused with the thorax, giving the entire body a more or less sac-like appearance. In many the body is marked by numerous transverse, fine lines, which are so impressed as to appear like the divisions between minute segments (Fig. 52). The majority of mites are very small; but some, as certain Ticks, are of considerable size.

With the exception of a single family the members of which bring forth living young, all mites are produced from eggs. As a rule, the newly-hatched mites have only three pairs of legs; but a fourth pair are added during growth. In Phytoptus, which infests plants, there are only two pairs of legs.

The mode of life of the different members of this order varies greatly: some are parasitic upon animals; others infest living plants; and many, feed upon dead animal or vegetable matter, thus acting as scavengers.

Among the mites that are parasitic upon animals are the various Ticks, which are very common in the warmer parts of our country. Figure 50 represents the Cattle-tick of the Southern States. It should be remembered in this connection that the so-called Sheep-tick is a true insect, belonging to the order Diptera.

The Itch-mite is a well-known parasite, infesting man and causing the disease known as the itch. The sensation characteristic of this disease is due to the burrowing of the mites in the skin; and the efficiency of sulphur ointment in checking this disease is due to the fact that by the use of it the mites are killed. Figure 51 represents an itch-mite greatly enlarged.

Parasitic mites are frequently found attached to insects; a common species occurs beneath the wings of locusts.

The best known of the mites that infest plants is the one commonly called the Red Spider. This lives upon house-plants; and in the warmer parts of the country, where there is a dry season, it infests fruit-trees in the open air. As it thrives only in a dry atmosphere, it can be subdued upon house-plants by a liberal use of water. When it occurs upon plants in the open air it can be combated with any of the washes found useful in destroying scale insects.

Some of the mites that infest plants produce galls. These galls are of various forms, but differ from those produced by gall-flies (Family Cynipidae of the Order Hymen-optera) in having open mouths, from which the young mites escape.

A common. disease of the pear, known as the pear-leaf blister, is produced by a four-legged mite, Phytoptus pyri (Phy-top'tus py'ri) (Fig. 52). The blisters characteristic of the disease are swellings of the leaf, within which there is a cavity affording a residence for the mites. Figure 53 represents a section of a leaf through one of these galls. Here the leaf is seen to be greatly thickened at the diseased part. On the lower side there is an opening through which the mite that started the gall entered, and from which young mites developed in the gall can escape, in order to start new galls. In addition to the swelling of both surfaces of the leaf its internal structure is seen to be modified. In some parts there is a great multiplication of the cells, and in others a large part of the cells have been destroyed. Two eggs of mites are represented in this gall. As the season advances, and the galls become dry and brownish or black, the thickening of the leaf becomes less marked. In fact, in some cases there is a shrinkage of the parts affected. Figure 54 represents a section through a leaf collected and studied in October.

Among the scavenger mites there are some that infest food products. Thus mites are sometimes found in cheese, in sugar, and in preserved meats.

The members of this class are air-breathing Arthropods, in which the head is distinct from the thorax, and the thorax and abdomen form a continuous region, with from six to two hundred segments, each bearing a pair of legs. The head bears a single pair of antennae.

The thousand-legged worms, as they are commonly called, are well-known and generally feared creatures. But few students find them attractive subjects of study; nevertheless it is well to know something about them, for some of them are dangerous animals, and some are harmless. A few species are injurious to agriculture, while others are to be classed among our friends. And all of them are of interest to the naturalist as representatives of a distinct type of Arthropods.

If we omit certain small and rather uncommon forms, the Myriapods may be classed in two orders; one consisting of the Centipedes, the other of the Millipedes.

The centipedes can be recognized at a glance by the fact that each segment of the body bears a single pair of legs (Fig. 55). The body is usually flattened, and the antennae are long and many-jointed.

Many species of centipedes are venomous. The poison glands open through the claws of the first pair of legs, which are bent forward so as to act with the mouth parts. These creatures abound in all parts of the United States; those which are found in the North are comparatively small, and rarely, if ever, inflict serious injury to man; but the larger species, which occur in the warmer regions, are said to be extremely venomous.

The centipedes are predaceous, feeding on insects; they usually live under stones, logs, and bark. There is one species, Cermatia forceps (Cer-ma'ti-a), which has very long legs, and only fifteen pairs of them, which is often found running on the walls of houses, especially in the Southern States. We have never heard of this centipede biting a human being, and as it feeds upon insects, especially cockroaches, it may be regarded as a welcome visitor in houses.

The millipedes differ from the centipedes in having two pairs of legs on each of the body segments except the first three. The body in most of them is not flattened as with the centipedes, and the antennae are comparatively short and few jointed (Fig. 56).

The millipedes, as a rule, live in damp places and feed on decaying vegetable matter. They are harmless, except that occasionally they feed upon growing plants.