442 SUPPLEMENT 



jaws, so that the nutritive fluids may be extracted. Besides, 

 we know that the scorpions, though without perforated man- 

 dibles, nevei'theless suck their prey in the same manner. 



The feet, in their relative size, vary, according to the dif- 

 ferent positions, habitual to these animals, and sometimes 

 even according to the sexes. They are inserted all around the 

 sides of the chest, and composed of seven articulations. The 

 last two constitute the tarsi, which are terminated by two 

 hooks. It is easy to conceive that these two hooks answer 

 the purpose to the arachnides of holding by their web, and 

 that they must also be useful in its construction. 



The spinning epeiras are the only animals of this family that 

 have the abdomen covered with a crustaceous or solid dermis, 

 folded in the form of a ring. In all the other species this part 

 of the body is soft, and without any apparent division. Its 

 envelope is only a sort of sac, in which the organs of circula- 

 tion, of respiration, the intestines, the vessels that secrete the 

 silk, and in the females the ovaries, and the other sexual parts, 

 are enclosed. Immediately under the dermis, the mucous 

 tissue is perceptible, composed of a soft matter, divided into 

 an infinite number of small grains. The heart is a large 

 vessel along the back, throwing out branches on each side. 

 The respiratory organs are t\\o in number, and composed of 

 small laminae, adherent to the interior parietes of two pouches 

 situated one at each side, near the base of the belly, and 

 covered by a membranaceous lid, leaving a transverse cleft, 

 for the passage of air. The place of these organs is usually 

 indicated by two yellow or whitish spots. 



The intestinal canal is straight. There is a first stomach, 

 composed of several sacs ; then, towards the middle of the ab- 

 domen, is a second stomachal dilatation, surrounded by the. 

 liver. The silk-vessels, usually six in number, extend, on each 

 side, along the whole interior: they resemble tortuous intes- 

 tines, filled with a yellowish matter ; contracted rather abruptly 



