structure, and can no longer work, but only fight. Some species go further and make slaves of the ants preyed upon. do all the work for their captors, even to making additions to their nest and acting as nurses to their young. The entire communal life of the ants seems to be based upon the perception of odor. If an ant of the same species but from a bers of the nest. The talking of ants (when they stop each other, when away from the nest, to communicate) is evidently a process of smelling, for they caress each other with the antennæ, the organs with which odors are above means the ichneumons save millions of dollars yearly to our country. REFERENCE BOOKS FOR THE PUPIL Davison, Practical Zoology, pages 52-68. American Book Company. Herrick, Text-book in General Zoology, Chap. XV. American Book Company. Jordan, Kellogg, and Heath, Animal Studies, Chap. XXII. D. Appleton and Company. Needham, Outdoor Studies. American Book Company. FOR THE TEACHER Comstock, Insect Life. D. Appleton and Company. Lubbock, Ants, Bees, and Wasps. D. Appleton and Company. 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. Spiders breathe by means of lunglike sacs in the abdomen, the openings of which can sometimes 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 spinneret. 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 building material which combines lightness with strength. Look carefully at a spider spinning and decide where the spinnerets are located. Tarantula on its back; p, poison fang; s. spinneret. USES AND FORM OF THE WEB -The web-making instinct of spiders forms an interesting study. Our common spiders may be grouped according 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 remaining away from the web. In other cases the spider hangs, back downward, under a thin sheet of filmy cross lines. The funnel-web makers form a closely woven web which is usually attached to glass or may be found in corners of a building. From one end of the For laboratory work see Hunter and Valentine, Manual, page 117. 2 Useful laboratory or home work may be given in the form of tabular comparisons between the various species of the arthropods. For examples of such tables see Hunter and Valentine, Manual, pages 116, 120, 127, 130. web a funnel-like tube runs downward and inward. In this tube the spider spends most of the time, running out to catch insects which may become entrapped. At the lower end of the tube is an opening through which the spider may escape in time of necessity. The funnel-web builders are strong-legged, active spiders. The orb-weaving spiders spin webs of geometrical exactness in bushes or long grass. They are usually of almost circular form with a spirally wound center thread supported on guy lines which are attached firmly to surrounding objects. These webs, which act both as homes and snares, are made of two kinds of silk, a supporting thread, tough but rather inelastic, and a thinner elastic sticky thread, out of which the snare is woven. The outer part of the web forms the snare. The central part of the web usually contains a shield of closely woven silk on which the spider may rest. Some orb weavers live near one edge of the web, hanging suspended within easy reach of a possible capture. In traveling over the outer part of the web the spider uses the guy lines only, as otherwise it might destroy its own web. Why? One of the commonest of the orb weavers is a large yellow and black spider known as Argiope. Their webs may be found in almost any garden or yard. How is it attached? How Look for the central shield on which the Find such a web. Describe its location. many guy lines does it contain? A poisonous centiped from Texas. Half natural size. From photograph by Davison. spider rests. Do you find a "winding stair"? Notice the open area between the central home of the spider and the outer or spiral zone of the web. This area, known as the free zone, gives opportunity for free movement around the web, as the spider does not travel on the sticky outer portion. Other Forms of Web. -Other forms of webs are seen in the wonderful nest of the trapdoor spider which, after excavating a hole in the ground, lines it with silk and then makes a lid of earth also lined with silk. This lid is closed by the spider after its retreat to the hole. Other spiders use the web for bridge building. In this case a long single strand is spun which is allowed to float off behind the spider into the air. This is flown like a HUNTER'S BIOL. 17 kite until it catches some projection, when the spider hauls in the slack, makes it fast, and travels across on the slender bridge thus built. Myriapods. - We are all familiar with the harmless and common thousand legs found under stones and logs. It is a representative of the group of animals known as the millepeds. These animals have the body divided into two regions, head and trunk. They have two pairs of legs for each body segment. The centipeds, on the other hand, have only one pair of legs to each segment. None of the forms in the eastern part of the United States are poisonous. CLASSIFICATION OF ARTHROPODA CLASS, Crustacea. Arthropods with limy and chitinous exoskeleton, breathing by gills, and having two pairs of antennæ. SUBCLASS I. Entomostraca. Crustacea with a variable number of segments, chiefly small forms with simple appendages. Some degenerate or parasitic. Examples, barnacles, water flea (Daphnia), and copepods (Cyclops). SUBCLASS II. Malacostraca. Usually large crustacea having nineteen pairs of appendages. Examples, American lobster (Homarus americanus), crab (Cancer), or shrimp (Palamonetes). CLASS, Hexapoda (insects). Arthropoda having chitinous exoskeleton, breathing by air tubes (trachea), and having three distinct body regions. Order, Aptera (without wings). Several wingless forms. Examples, springtails. Order, Orthoptera (straight wings). Example, Rocky Mountain locust. Order, Lepidoptera (scale wings). Examples, cabbage butterfly, cecropia moth. Order, Diptera (two wings). Examples, house fly, mosquito. Order, Hemiptera (half wing). Order, Neuroptera (nerve wings). Examples, all true bugs, plant lice, and cicada. Order, Hymenoptera (membrane wings). Examples, bees, wasps, ants. CLASS, Myriapoda. Arthropoda, having long bodies with many segments; one or two pairs of appendages to each segment. Breathing by means of tracheæ. Example, centiped. REFERENCE BOOKS FOR THE PUPIL Needham, Outdoor Studies. American Book Company. FOR THE TEACHER Emerton, The Structure and Habits of Spiders. Knight and Millet. |