46 THE LIFE-STORY OF INSECTS [CH. 



body and consists of a gullet, stomach (mid-gut), 

 intestine, and rectum; it Is adapted for tin- diuvstion 

 of solid food. In the butterfly there is one outgrowth 

 of the gullet in the head a pharyngeal sac adapted 

 for sucking liquids ; and another outgrowth at the 

 hinder end of the gullet (which is much longer than 

 in the larva) a crop or food-reservoir lying in the 

 abdomen. The intestine of the butterfly also is 

 longer than that of the larva, being coiled or twisted. 

 Towards the end of the last larval stage, the cells of 

 the inner coat (epithelium) lining the stomach begin 

 to undergo degeneration, small replacing cells ap- 

 pearing between their bases and later giving rise to 

 the more delicate epithelium that lines the mid-gut 

 of the imago. The larval cells are shed into the 

 cavity of the stomach and become completely broken 

 down. J. Anglas (1902), describing these microscopic 

 changes in the transformations of wasps and bees, has 

 shown that the tiny replacing cells can be recognised 

 in sections through the digestive canal of a very young 

 larva ; they may be regarded as representing imaginal 

 buds of the adult gastric epithelium. In the trans- 

 formations of two- winged flies of the bluebottle group, 

 A. Kowalevsky (1887) has shown that these replacing 

 cells are aggregated in little masses scattered at 

 different points along the stomach and thus cor- 

 responding rather closely to the imaginal discs of 

 the legs and wings. 



