364 DIPTERA. 



lated in great numbers, and remain until the larvai are sufH- 

 ciently developed to be hatched, so that these animals are 

 viviparous. In the pupiparous HippobosciB, the female organs 

 are formed on an entirely special type, corresponding with the 

 remarkable mode of reproduction in these animals." (Siebold.) 

 Near the external opening of the oviduct is a pair of glands 

 designed to secrete the gummy matter coating the eggs. 



The eggs of the Diptera are usually cylindrical, elon- 

 gated and slightly ciu'ved, and the surface is smooth, not being 

 ornamented as in the Lepidoptera. In the Tipulidcn the 

 eggs become mature as soon as the pupa skin is thrown off, 

 when they are immediately laid. 



The larvffi are footless, white, fleshy, thin skinned, cylindrical 

 and worm-like, spindled or linear in shape. Thej^ have, in the 

 higher families, as in the Tij^ulidce, a distinct head ; but they 

 are often headless, as in the Mtiscidce , and are then called 

 maggots. They live in mould, decaying organic substances, or 

 in the water. Many maggots are provided with two corneous 

 hooks, probably the mandibles, with which they seize their food. 

 The pupa is either naked (Pupa obtecta. Fig. 276), like the 

 chi-ysalids of moths, with the limbs exposed, as in the Tipu- 

 lidce ; or they are coarctate (pupa coarctata, Fig. 

 272) as in the flies generally, the skin of the larva 

 serving to protect the soft pupa within, as during 

 the growth of the pupa the old larval skin separates 

 from the newly formed pupa skin, which contracts 

 slightly. It is then called the puparium, and is 

 usually cylindrical and regularly rounded at each end 

 like the cocoon of moths. Tliose which have the 

 pupil? obtected, when aquatic and active, are provided 

 with gill-like filaments permeated with tracheae. 



The semipupa stage of Diptera, corresponds generally with 

 that of the Ilymenoptera and Lepidoptera. By an ingenious 

 device Dr. Fitcli succeeded in observing in the living insect 

 the processes by which the larva of the willow Cecidomyia 

 (C. salicis) turns to a pupa, and which is usiuilly accomplished 

 during the night. He states that "as the first step of this 

 change, at the anterior end of the larva the c^^tis or opake 

 inner skin becomes wholly broken up and dissolved into a 



