(88) 



528 C. GORDON HEWITT. 



distance from their origin they bifurcate and the resulting 

 four tubules have a convoluted course, being mingled to a 

 great extent with the adipose tissue. They are similar in 

 appearance and histologically to those of the imago, consisting 

 of large cells, of which only two can be seen usually in section ; 

 they consequently give the tubules a moniliform appearance. 

 In the mature larva these cells appear to break down to form 

 small deeply-staining spherical bodies. This histological 

 degeneration begins at the distal ends of the tubules, which in 

 the mature larva usually have the appearance shown in fig. 28 

 (m. t.) ; all the stages of degeneration can be traced out. 

 This process may be a means of getting rid of the remaining 

 larval excretory products. 



The four caeca at the anterior end of the ventriculus have 

 already been described. 



5. THE RESPIRATORY SYSTEM. 



The tracheal system (fig. 26) of the adult larva consists of 

 two longitudinal tracheal trunks united by anterior and 

 posterior commissures, and communicating with the exterior 

 by anterior and posterior spiracles, the latter are situated in 

 the middle of the oblique caudal end, and the anterior spiracles, 

 which are not present in the first larval instar, are situated 

 laterally at the posterior border of the third body-segment. 



I believe that the anterior spiracles (a. sp.) are true func- 

 tional spiracles, though for some time I shared Lowne's 

 opinion that they were not functional. This latter view was 

 due to the fact that it was difficult to understand how these 

 spiracles could obtain air when they are immersed, as they 

 usually are, in the moist fermenting materials on which the 

 animal feeds. A careful examination of their structure, how- 

 ever, strengthens my belief that they are able, if necessary, 

 to take in air ; the occasions when this is possible are 

 probably not infrequent. Each of the anterior spiracular 

 processes consists of a fan-shaped body (fig. 9, a. sp.) bearing 

 six to eight small papilliform processes. The papillas (fig. 7) 



