FLIES WITH AQUATIC LARV^ 



171 



retractile tail. It can, how- 

 ever, be distinguished from 

 Eristalis by the much more 

 complete head, and by the 

 presence of two slender ap- 

 pendages, one at each side 

 of the root of the tail. A 

 minute examination reveals 

 many other points of dif- 

 ference ; indeed, the two 

 larvae only resemble one 

 another in certain super- 

 ficial characters, which im- 

 mediately depend upon 

 their similarity of habitat. 



The head of the larva 

 is hard and small, not un- 

 like that of the Chironomus 

 larva, but with many differ- 

 ences of detail. There is 

 a pair of eye-spots, and two 

 minute antennae, which can 

 only be made out by close 

 examination. The mouth- 

 parts are a good deal like 

 those of Chironomus. 



Behind the head come 

 twelve segments, and it is 

 necessary to notice how 

 these are adapted to the life 

 of an animal which has to 

 creep in and through mud. 



B 



Fig. 56. — A, I arva of Ptychopterapalu- 

 dosa ; B, tail of larva of Ptychoptera, 

 much magnified, showing convoluted 

 air-tubes and lateral appendages. 



