47 



ending in a vnnged state. A spider differs from an insect in almost all these particulars- 

 1st. It is divided into only tioo segments. 2nd. It breathes, as a rule, through sacs in 

 the abdomen. 3rd. It has no distinct head separate from the thorax, and possesses no 

 antennae. 4th. It has eicjht articulated legs. 5th. It undergoes no distinct metamor- 

 phoses, and never attains wings. On all these accounts, then, we cannot scientifically call 

 a spider an insect, though it is often convenient to use the term in ordinary conversation. 

 A spider technichally belongs to the class Arachnida, which includes also the scorpions 

 and mites ; from the two latter orders it is distinguished especially by its spinnino' organs 

 and its faculty of making cobwebs and silk cocoons for its eggs. 



2. — Anatomy.* 



The common round-web spider, Ejnira vulgaris^ Hentz, will serve as well as 

 any other species to show the anatomy of s])iders in general. Figure 7 shows the 



under side of the spider ; Figure 10 the upper 

 side ; and Figure 1 1 an imaginary section through 

 the body, to show the arrangement of the inter- 

 nal organs. To begin with Figure 7, the body is 

 seen to be divided into two parts connected only 

 by the marrow joint. A, just behind the last pair 

 of legs. The front half of the body, called the 

 Thorax, contains the stomach, the central part of 

 the nervous system, and the large muscles which 

 woi-k the legs and jaws. The hinder half, the 

 Abdomen, contains the intestine, the breathing 

 organs, the principal circulating-vessels, the or- 

 gans of reproduction, and the spinning-organs. 

 Connected with the thorax are six pairs of limbs, 

 four pairs of legs, B B B B, a pair of palpi, C, 

 and a pair of mandibles, D. 



The Legs are used chiefly for running, jumping 

 and climbing ; but the front pair serve often as 

 feelers, being held up before the body, while the 

 spider walks steadily enough on the other six. 

 One or both of the hinder legs are used to guide 

 the thread in spinning ; the spider at the same 

 time walking or climbing about with the other six 

 or seven. The legs are seven-jointed ; and on 

 the terminal joints are three claws. Fig. 8, A, B, 

 C, and various hairs and spines. In many spi- 

 ders a brush of hairs takes the plac3of the middle 

 claw, as in the jumping- spiders, Fig. 9. Spiders 

 with these brushes on their feet are able to walk 

 up a steep svirface or under a horizontal one, bet- 

 ter than those with three claws. The legs of 

 most spiders have amongst the hairs moveable 

 spines, which, when the spider is running about, 

 extend outward at a right angle with the leg, and 

 I'ig- 7. when it is resting are closed against the skin. 



In front of the legs are the Palpi, Fig. 7, C C, — a smaller pair of limbs, with six joints, 

 and only one claw, or sometimes none. They are used as feelers, and for handling food, and in 



* As the writer has stated at the outset that this paper is merely a compilation, he does_ not think it 

 necessary to indicate by quotation marks, or otherwise, those portions that are taken verbatim from the 

 authors referred tn. Those who are familiar with their works will have no difficulty in verifying the pas- 

 sages should they desire to do so. 



