THE CATERPILLAR AND THE MOTH 



it leaves the pupal skin projecting from the mouth of the 

 cocoon (Plate i 2). 



Concurrent with the remodeling in the external form of 

 the insect, other changes have been taking place within the 

 body. The first of the complicated metamorphic processes 

 that affect the inner organs occurs in the stomach, where, 

 as we have already observed, the inner wall is cast off at 

 about the time that the caterpillar begins the spinning of 

 its cocoon. This shedding ot the stomach lining is quite a 

 different thing from the molting of an external cuticula, 

 for the stomach wall is a cellular tissue. Furthermore, 

 wherever other cell layers are discarded, as in the case of 

 the epidermis, the cells are absorbed into the body cavity. 

 A new stomach wall is generated usually from groups of 

 small cells that originally lay outside the old wall and were 

 retained when the latter was cast off. These cells, as do 

 the imaginal discs of the epidermis, form a new lining. to 

 the stomach and give a new shape to this organ, which in 

 the adult insect may be quite different from that of the 

 larva. The shedding of the stomach wall is not necessarily 

 a part of the metamorphosis, for in some insects and in 

 certain other related animals, it is said, the stomach 

 epithelium as well as the cuticular lining is shed and 

 renewed with each molt of the body wall. 



The parts of the alimentary canal that lie before and 

 behind the stomach, that is, the oesophagus and crop 

 (Fig. 154, Of, Cr) and the intestine (hit), formed in the 

 embryo as ingrowths of the body wall, are regenerated 

 from groups of cells in their walls in the same manner as is 

 the epidermis itself, the old cells being absorbed into the 

 body. The cuticular linings of these parts are shed with 

 the cuticula ot the body wall at the time of the molt. The 

 complete alimentary canal of the moth is very different 

 from that of the caterpillar, as will be shown in the next 

 section of this chapter (Fig. 164). 



The walls of the Malpighian tubules are said to be 

 regenerated in some insects, but the tubules do not change 



[299] 



