120 Development within the Larva 



infolclings of tlie epidermis, but at times tlieir real 

 character is not evident without close inspection. They 

 may penetrate far below the surface, and the invaginated 

 layer, which connects them with the rest of the epidermis, 

 may be hardly visible. The infolded cells may proliferate, 

 and form solid masses within the body. Hence the name 

 of hnaginal discs, originally applied by Weismann to 

 complex structures of this sort. 



The chief alterations which are necessary to convert the 

 larva of Chironomus into a flying 

 insect are these. Biting mouth- 

 parts are -replaced by suctorial 

 ones, suited to the nourishment 

 of an insect which must not be 

 loaded with food nor spend 

 much time in feeding. In our 

 common English species of 

 Chironomus the fly does not feed 

 at all, but the adaptation to a 

 change of food takes place not- 

 withstanding, and the mouth- 

 organs of the fly, though not 

 functional, are formed as in cer- 

 tain other Diptera which still 

 occasionally feed upon the honey 



pairs). met, metathorax (two ^f ^p^j^ flowCrS (Tipula, Bibio, 



&c.). The eyes and antennae, 

 which were rudimentary in the burrowing larva, become 

 large and complex. "Wings and long thoracic legs are 

 developed. The hinder abdominal segments become 

 modified for reproduction. The fly no longer inhabits the 

 water, and it breathes by tracheae with open spiracles 

 instead of by organs of aquatic respiration. Every part 

 of the body undergoes change, and all the external organs 

 are completely recast. 



Fig. 89. — Early state of ima- 

 ginal rudiments, from tiiorax 

 of living larva, pro, protliorax 

 (with one pair of rudiments 

 only). mes, niesothorax (two 



