MOULTING HABITS OF SPIDERS. 



99 



herself upon the third pair in unsheathing the fourth, upon the second to 

 free the third, and so on. 



The abdomen does not commence to moult until after the cephalothorax. 

 It is disengaged from the skin, without the aid of the legs, by means of 

 contractions of the abdominal muscles, which produce undulatory move- 

 ments of the skin in the direction from the cephalothorax toward the 

 spinnerets. The cast skin of the abdomen is always much wrinkled, owing 

 to its extreme softness and fineness, that permits it to fold up under 

 pressure. In this saclike abdominal moult one finds the moulted lungs and 

 glands, and fragments of the moult of the intestine and muscles. (Wagner.) 

 The skin of Mygale when cast is sometimes so little broken, as shown 

 by Fig. 63, that by placing the corselet shell upon the sternum and pasting 



it down to the falces, a casual observer might think it a living 

 Mourt;^ creature. It will be seen from the cut that the abdomen has 



been withdrawn from the old tegument forward through the cir- 

 cular rent at the base, where it was united to the pedicle. Even the long 

 spinnerets retain their hab- 

 itual position curled upward 

 along the apex. The ab- 

 dominal skin of this spi- 

 der is so much thicker than 

 that of ordinary araneads, 

 and withal is so heavily cov- 

 ered with strong hairs, that 

 it more readily retains its 

 usual form, instead of 

 shrinking up in a wrinkled 

 mass, as with most species. 

 Sometimes, however, the cast 

 is not so complete as here shown. In this figure the line of rupture 

 along the sides of the cephalothorax is well shown; also the usual mode 

 in which the pedicle is parted, uniting the abdomen on the one hand and 

 the corselet on the other to the sternum. The mandibles have evidently 

 been withdrawn backward by a motion the reverse of the abdomen, as 

 shown by the unbroken moult fallen forward upon the moult of the mouth 

 parts which adhere to the sternum. 



V. 



Some spiders issue from the eggs with their feet free ; others, as 

 Epei'roids and Theridioids, come out having their feet adhering under the 

 abdomen. They remain thus for six days, more or less, when they cast the 

 first tegument and quit the cocoon. ^ The skin thus enclosing the legs is 



Pifi. 63. A cast skin of Mygale, showing slight rupture of parts. 



Simon, Histoire Naturelle des Araign^es. 



