the rest, collected into a packet, and cast off. Mr. Rennie, the author of a very interesting book on insect architecture, describes a process of this kind which he observed on board of a steam-boat. It was a geometric Spider, that is, one that forms its web of regular circular lines. The web or net was covered with flakes of soot. "Some of the lines," he says, "she dexterously stripped of the flakes of soot adhering to them; but in the greater number, finding that she could not get them sufficiently clean, she broke them quite off, bundled them up, and tossed them over. We counted five of these packets of rubbish which she thus threw away, though there must have been many more, as it was some time before we discovered the manœuvre, the packets being so small as not to be readily perceived, except when placed between the eye and the light. When she had cleared off all the sooted lines, she began to replace them in the usual way.

515. Many observations have been made, and experiments tried, to determine how Spiders transport themselves from tree to tree, across brooks, or even sometimes through the air, without any visible starting-point. The subject is not entirely cleared up, but it is well ascertained that they spin out the thread, letting the wind take it, trying it occasionally with the feet to decide whether the farther end has attached itself to any object. So soon as the Spider finds by pulling on it that it is fastened, it runs along upon it, strengthening its cable by spinning another as it goes. Spiders have not, as some have supposed, the power of projecting their lines in opposition to the moving air, but they uniformly put their bodies in such position that the line may go with the air, that is with the head toward the direction from which the breeze comes. They watch the wind as much as the sailor does. The little gossamer Spiders let their lines, like balloons, carry them off into the air, breaking loose from the objects on which they stand when they

feel themselves acted upon by a force sufficient for that purpose. They may thus be seen mounting aloft from the tops of twigs and blades of grass, from fences, etc.

516. The architecture of Spiders has considerable variety. That of the house Spider and that of the common geometric Spider are familiar to every one. That of the labyrinthic Spider is very curious. Its nest may be seen spread out a broad sheet on hedges, furze, low bushes, and sometimes on the ground. "The middle. of this sheet," says Rennie," which is of a close texture, is swung, like a sailor's hammock, by silken ropes extended all around to the higher branches; but the whole curves upward and backward, sloping downward to a long funnel-shaped gallery which is nearly horizontal at the entrance, but soon winds obliquely till it becomes quite perpendicular. This curved gallery is about a quarter of an inch in diameter, is much more closely woven than the sheet part of the web, and sometimes descends into a hole in the ground, though oftener into a group of crowded twigs or a tuft of grass. Here the Spider dwells secure, frequently resting with her legs extended from the entrance of the gallery, ready to spring out upon whatever insect may fall into her sheet-net."

517. There are some species of spiders that build their nests of clay, which they knead into due shape, and hence are called Mason Spiders. There is one of these found in the West Indies. This Spider digs a hole obliquely in the earth about three inches deep and one inch in diameter, the walls of it being made of clay. This cavity it lines with a thick web, which, when taken out, resembles a leathern purse. This tapestried chamber has a very singular door. It is made of about a dozen layers of this same lining, closely united together, and has a hinge of the same material. In Fig. 238 (p. 305) is represented the nest of another Mason Spider found in France, A being the nest shut, and B the nest open;

C the Spider, D the eyes magnified, and E and F parts of the foot and claw magnified.

518. There is a Spider common in the woods that weaves together a great many leaves for a dwelling, and in front of this spreads its snares to catch its prey. When winter approaches it leaves its eggs in this nest to be hatched the following spring, and itself retires to some hollow tree to die.

519. An English clergyman, Mr. Shepherd, has often seen in the fen ditches of Norfolk a very large Spider that makes a raft by fastening weeds together with silken threads, and sails forth on this in search of insects that may chance to get into the water. But the most interesting water-spider is one that makes for itself a silken diving-bell, which looks in the water like a little silver globe. This is sometimes partly above the surface of the water, but at others it is fastened by silken ropes to objects below. The Spider contrives in some way to carry

air down to its diving-bell, coming up every now and then to the surface for this purpose.

520. I have already said enough of the Scorpions (§ 509), and on the second group of the Arachnida I will spend but a few words. Among the Mites is the animal which occasions the disease called the itch, an enlarged representation of which you have in Fig. 239. It has an

or Acarus of the Itch.

oval body, a mouth armed with bristles, and eight feet, four of which have suckers at the end. There is a great variety of mites which are found on plants and animals, and some live in the water, swimming about with great freedom. The scarlet Mite of our gardens has a most brilliant scarlet color. The Harvest-men, so appropriately called Father-long-legs, as they have, perhaps, longer legs than any other animal of any kind,

Fig. 239.---Sarcoptes Scabiei, are mostly very agile. The Book Scorpions, so called, are little Arachnida which inhabit herbariums, old books, etc. They are good runners, often going sidewise like crabs, and they hunt the minute insects which are found in such situations.

Questions.-How do the Arachnida differ from insects? What is said of their food? What of their means of killing their prey? What is said of those which are parasitical? What is said of the Scorpions? What are the two groups of the Arachnida? What are the two chief purposes for which Spiders spin? What other purposes are sometimes accomplished by it? What is said of the cocoons which some Spiders spin? Describe the spinning apparatus of Spiders. What is said of the compound character of the Spider's thread? Why is it not spun whole? What is said of the mode of its attachment? Describe the foot of a Spider. What is the use of the combs in it? Describe its mode of repairing its web. What is known of the manner in which Spiders transport themselves from one spot to another

by their threads? What is said of the Gossamer Spiders? Describe the architecture of the Labyrinthic Spider. What is said of the Mason Spiders? What of the Spider that weaves leaves together? What of the Spider that builds a raft? What of the Diving-bell Spider? What are some of the Arachnida of the second group? What is said of the Mites? What of the Harvest-men? What of the Book Scorpions?

CHAPTER XXXI.

CRUSTACEANS, AND THE WORM AND LEECH TRIBE.

521. THE class of the Articulata called Crustacea has its name from the Latin word crusta, a crust or shell. It includes Lobsters, Crabs, Prawns, Shrimps, Sowbugs, Sand-fleas, Barnacles, etc. Lobsters and Crabs are the most perfect animals of the class.

522. There is considerable resemblance to insects, and also to Spiders, in most of these animals. Like the Insects, they may be divided into two groups-the mandibulate and the haustellate. The eyes of the Crustacea are generally compound, like those of the Insects. They have also antennæ. But the Crustacea differ from insects in the character of their respiratory apparatus. They are aquatic animals, and breathe by gills. There are a few species that are formed to live in air. The Land Crabs, found mostly in the Antilles, are an example. In them there is, above the gills, a spongy apparatus, from which continually exudes a moisture that keeps the gills from becoming dry.

523. The legs of the Crustacea often amount to seven pairs, as in the Woodlouse and Sandhopper; but in other cases there are five pairs, as in the Crab. The legs are constructed very differently in the various Crustacea, according to the manner in which they are to be used. In some they are leaf-like membranes, being thus fitted for swimming; in others they are columns jointed together, to be used only in walking; in others they are so