. Elements of biology; a practical text-book correlating botany, zoology, and human physiology. Biology. XX. SPIDERS AND MYRIAPODS. Structure of the Spider. — Use any large spider for the following work, preferably Argiope, the brightly colored garden spider.* Examine the large spider carefully. Notice that it differs from an insect in having the head and thorax joined together to form a cephalothorax. Notice the number of legs; here is another difference from insects. Look on the dorsal side of the cephalothorax. The glistening black objects are simple eyes, of which there are usually four pa
. Elements of biology; a practical text-book correlating botany, zoology, and human physiology. Biology. XX. SPIDERS AND MYRIAPODS. Structure of the Spider. — Use any large spider for the following work, preferably Argiope, the brightly colored garden spider.* Examine the large spider carefully. Notice that it differs from an insect in having the head and thorax joined together to form a cephalothorax. Notice the number of legs; here is another difference from insects. Look on the dorsal side of the cephalothorax. The glistening black objects are simple eyes, of which there are usually four pairs. What is the number and position of eyes in this specimen? Make a diagram. Argiope breathes by means of lung- like sacs in the abdomen, the openings of which can some- times be seen just behind the most posterior pair of legs. Another organ possessed by the spider, which insects do not have (except in a larval form), is known as the spin- neret. This is a set of glands which secrete in a liquid state the silk which the spider spins. On exposure to air this fluid hardens and forms a very tough build- ing material which combines lightness with strength. Look carefully at a spider spinning and decide where the spinnerets are located.^ Uses and form of the Web. — The web-making instinct of spiders forms an interesting study. Our common spiders may be grouped accord- ing to the kind of home they build. The web in some cases is used as a home, in others it forms a snare or trap. In some cases the web is used for ballooning, spiders having been noticed clinging to their webs miles out at sea. The webs seen most frequently are the so-called cobwebs. These usually serve as a snare rather than a home, some species remain- ing away from the web. In other cases the spider hangs, back down- ward, under a thin sheet of filmy cross lines. The funnel-web makers form a closely woven web which is usually attached to grass or may be found in corners of a building. From one end of the * Fo
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