The Life of Spiders 



this habit of cannibalism is has not been determined. McCook 

 states that the young of the orb-weavers prey upon each other 

 after they leave the egg-sac. 



The moulting of the cuticula. — Spiders, like insects, shed, from 

 time to time, an outer layer of the cuticula of the body. This 

 process is termed moulting and the cast skin is called the exuviae. 

 The number of the moults and the intervals between them varies 

 with different species, and has been determined in only a few cases. 

 Blackwall states that Epeira catophylla moults five times and 

 Tegenaria civtlis, nine times. Wagner found that the young of 

 Trochosa singoriensis moulted four times before beginning to lead 

 .in independent life. 



The cuticula of the cephalothorax and of its appendages, 

 the legs and mouth-parts, is 

 firm and inelastic, being 

 hardened by a horny sub- 

 stance known as chitin. Ow- 

 ing to this it will not stretch 

 enough to allow for the growth 

 of the spider. The result is, 

 that from time to time, the 



. . . ,. Fig. 182. TARSUS OF A MOULTING SPIDER 



cuticula becomes too small dolomedes scrtpti 



for the spider and must be 



shed. But before this is done a new cuticula is formed beneath 

 the old one; then the old skin bursts open, and the spider 

 casting it off is clothed in a soft skin, which stretches to accom- 

 modate the increased size of the body. Very soon, however, 

 this new skin becomes hardened with chitin, and after a time it 

 in turn must be shed. 



Before the old cuticula is shed it is loosened by a fluid, the 

 moulting fluid, which is excreted from glands that open through 

 the new cuticula. Figure 182 represents the tarsus of a moulting 

 spider; here the old skin can be seen separated from the new ; 

 this is especially clear in the region of the claws, there being 

 apparently two pairs of claws; but the outer pair is merely the 

 loosened cuticula of the claws. 



After the old cuticula is loosened, it splits along the sides 

 of the body and in front of the eyes; the slit being just above the 

 base of the legs and mouth-parts and extending back on each 

 side upon the abdomen. I hat portion of the old cuticula that 



183 



