682 



TEXT-BOOK OF ENTOMOLOGY 



of rings (v and K) of imaginal tissue. The imaginal ring of the 

 fore-intestine (v) lies in the region of the proventriculus (pr, com- 

 pare Fig. 635, im), while that of the hind-intestine is situated 

 directly behind the base of the urinary tubes. The regeneration 

 of these two parts of the digestive canal is not entirely accomplished 

 by these two rings, but the imaginal rudiments of the neighboring 

 parts of the outer surface of the body also have a share in it. Thus 

 it appears that the foremost part of the O3sophagus is built up from 

 the imaginal buds in the region of the mouth, 



while the imaginal buds surrounding the \$$ 0? 



anus in the 8th abdominal segment (Fig. 633, 



-/ 



m> 



o 



m 



FIG. 634. Cross-section through the mid-intestine of 

 pupa of Musca: e, rejected and degenerate epithelium of the 

 larval stomach; /, cellular layer newly formed around the 

 same ; m, muscular layer ; m', imaginal cell of in ; o, imaginal 

 bud of the mid-intestinal epithelium ; t, tracheal stem. 

 After Kowalevsky, from Korschelt and Heider. 



FIG. 685. Longitudinal sec- 

 tion through the proventriculus 

 of a muscid larva : im, fore- 

 intestinal, imaginal ring ; oe, 

 oesophagus; pr, proventriculus. 

 After Kowalevsky, from Kor 

 schelt and Heider. 



ims) produce by invagination the rectal pouches, together with the 

 rectal papillae. 



The formation of the mid-intestine (stomach) takes place in such 

 a way that the island-like imaginal buds spread out by cell-multi- 

 plication over the outer or basal surface of the larval mid-intestinal 

 epithelium (Fig. 634, o), until they finally unite, so as to form the 

 wall of the imaginal mid-intestine (stomach). At the same time 

 the entire larval epithelium (e) is cast in the interior and forms the 

 so-called yellow body, which becomes surrounded by a layer of small 

 cells and a jelly-like mass, and remains until its destruction in the 

 pupal stomach. The larval muscular layer (m) remains intact as 

 long as the imaginal mid-intestine is not fully developed, when 



