Imaghial Folds of Head 



T27 



AVe liave specially studied tlie development of the head imagiimi 

 of the imago within the larval head, and the following hQil!" 

 account is largely taken from our paper of 1892. 



In larvae about half an inch long the epidermis of the 

 top of the head begins to 

 be infolded along two 

 longitudinal lines, which 

 run forwards from the 

 junction of the head and 

 thorax, diverging a little 

 as they do so. These lines 

 correspond to the margins 



of the clypeUS in the larval Fig. 97.— Early state of invagination 

 1 -, YT\\ • 1 -1 ^'^^ imaginal antenna, from larva, divided 



nead. llie epidermis, thus along middle line. /, longitudinal in- 

 carried into the interior, ""^ "" 



gives rise to new cuticular organs, first to the pupal 

 cuticle, and subsequently to the various external organs 

 of the head of the fly. 

 The cuticle of the head 

 of the jmpa is of less 

 interest, and its for- 

 mation need not be 

 23articularly described. 

 The comj)ound eye and 

 antenna of the fly 

 originate in these epi- 

 dermic folds, and are 



therefore developed at ^."^ 98. -Trans verse section through invagi- 



r nations tor imagmal head (early state). The 



a distance from the section passes through the junction of the head 



and prothorax. c, larval cuticle, y, longitu- 

 larval cuticle, though dinal fold, a, antenna of imago, dv, dorsal 



vessel, ces, oesophagus. 



they are from the first 



external in their morphological position. The outer wall, 

 the bottom, and ultimately the inner wall of each invagi- 

 nation develop facets, and thus give rise to the compound 

 eye of the fly. In the larva this compound eye looks into 



