THE DIGESTIVE CANAL 



681 



intact from the larva to the imago. Indeed, the dissolution of the 

 muscles is the first process which occurs in the metamorphosis. 

 The destruction of the larval muscles is accomplished in such a way 

 that a great number of leucocytes 

 which have collected on the sur- 

 face of the muscular fibres, press 

 through the sarcolemma and 

 enter within the muscular tissue, 

 filling the spaces formed between 

 them. By this means the mus- 

 cles break up into a number of 

 rounded particles which are 

 taken into the interior of the 

 leucocytes. Thus a collection 

 of granule-balls arise from the 

 muscles, which finally separate 

 from each other and become 

 scattered throughout the body- 

 cavity of the pupa. In the same 

 way as the muscular substance, 

 the muscle-nuclei are taken up 

 and digested by the phagocytes. 



The imaginal muscles develop 

 from the definitive mesoderm 

 which has originated from the 

 mesoderm of the imaginal buds 

 (Fig. 632, (7, m). 



The digestive canal. As in 

 the hypodermis and muscles, 

 the histolysis of the larval diges- 

 tive tract and its new formation 

 from separate imaginal buds go 

 on simultaneously, so that the 

 continuity of the process is not 

 interrupted. 



The imaginal buds of the 

 much-shortened pupal digestive 

 canal occur in the mid-intestine 

 (stomach) in the form of numer- 

 ous scattered groups of cells 

 (Fig. 633, ie}, and in the fore- 

 and hind-intestine in the form 



FIG. 688. Digestive tract of a Musca larva 

 with the imaginal germs : bd, coeca ; s, food- 

 reservoir ; is, imaginal ring of the salivary gland 

 (ftp) ; f, fat-cells at the end of the salivary gland ; 

 pr, proventriculus ; r, its ring ; ie, imaginal 

 cells of the mid-intestinal epithelium ; cA, chyle- 

 stomach ; ma, urinary tubes ; im, imaginal 

 cells of the mid-intestinal, muscular layer ; ims, 

 hinder, abdominal, imaginal buds ; h, hind in- 

 testinal, imaginal bud; M, hind-intestine. 

 After Kowalevsky, from Korschelt and Heider. 



