The Life of Spiders 



had covered the dorsal aspect of the cephalothorax is lifted off 

 like a lid and remains attached to the abdominal portion (Fig. 

 182 bis). Through the opening thus made the body is worked out, 



and the appendages 

 one after the other are 

 pulled from their old 

 coverings. 



In addition to the 

 mechanical reason for 

 the moult, the allow- 

 ing of the increase in 

 size of the body, there 

 are doubtless physi- 

 ological reasons for it 

 also. In spiders the old 

 cuticula of the abdomen 

 is about as elastic as the 

 new one, still the moult 

 includes this part of the 

 body as well as the fir- 

 mer portions. At each 

 moult the spider is 

 clothed with a complete coat of new hairs. When the function 

 of the hairs as sense organs is considered, it is seen that their 

 renewal at intervals is very important. Other physiological 

 reasons for the moult have been suggested, but as yet they are 

 not well understood. 



Transformations. — In the course of their development, 

 spiders undergo comparatively slight changes in form. Their 

 development is comparable to that of those insects that undergo 

 an incomplete metamorphosis. They increase in size, and the 

 proportions of the different parts of the body undergo a greater 

 or less change; but there is no marked change in form as there 

 is with those insects that undergo a complete metamorphosis. 



The most marked change takes place at the last .moult, when 

 the development of the sexual organs is completed. Previous 

 to this moult, the tarsus of the pedipalp of the male is merely a 

 club-like segment in appearance; but when the cuticula is shed 

 for the last time, the exceedingly complicated organ already 

 described is disclosed. So also in the case of the female of those 



Fig. 182 bis. MOULTED SKIN OF A SPIDER, 

 DOLOMEDES URINATOR, MALE 



184 



