CLASS ARACHNIDA 



297 



Certain cave spiders are blind. The legs often have pads of hairs between 

 their terminal claws which enable the animal to cling to walls and ceilings. 



At the posterior end of the abdomen are the spinning organs, con- 

 sisting of two or three pairs of spinnerets (Fig. 193), which are finger-like 

 appendages, sometimes jointed. At the tip of each of these spinnerets 

 open many small spinning tubes, from which 

 the silk is spun. The silk is secreted in glands 

 within the body and passes out in a liquid 

 condition, hardening as soon as it comes in 

 contact with the air. The anal opening lies 

 just posterior to these spinnerets, and just in 

 front of them may be a single spiracle. On 

 the ventral surface of the abdomen anteriorly 

 are three openings. In the median line is 

 the genital opening, protected in the female 

 by a plate known as the epigynum; and on 



each side, a slit placed transversely, which is head of Lycosa caroiinensis 

 the opening into an air sac. The spiracle SiiTroin. NeilrX/'xt 

 may be farther forward than stated above, 

 and there may be two just behind the genital opening. 



322. Internal Structures. — The alimentary canal includes a narrow 

 esophagus, a sucking stomach, a digestive stomach, and an intestine 



Chelicera 



aw 



Fig. 194. — Front view of 



Pericafdial 

 cavify ~ 



Intestine with 

 complexly branched 

 diverticula /Heart 



Ma/pighian 

 tubules 



Stercoral 

 pocket 



Poison gland 



C:?^^\/^ '°^''r\ Tn.cbei3lfnds//Anus 



r, -/• / -neiicera^-M^ / „ \ ■ ^ Spinnerets 



Pedipalpus stumps of legs ^^^.J %^^ffj^ 



receptacle 

 FiQ. 195. — Median section of a female spider, diagrammatic, to show internal structure. 

 {From Comstock, "The Spider Book"; copyright, 1912, by Doubleday, Doran & Company, 

 Inc.) The nervous system in the cephalothorax is stippled, as is also the reproductive 

 system in the abdomen. The heart is crosslined and the blood vessels in black; the poison 

 gland and duct are also black. The malpighian tubules are finely crosSlined and the spin- 

 ning glands and ducts shaded. The alimentary canal and diverticula are white. 



(Fig. 195). Malpighian tubules empty into the intestine near the 

 posterior end. The circulatory system consists of a heart, lying in a 

 pericardial cavity situated dorsally in the abdomen; and of arteries, 



