364 DIPTERA. 



lated in great numbers, and remain until tlie larvae are suffi- 

 ciently developed to be hatched, so that these animals are 

 viviparous. In the pupiparous Hippoboscse, 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 curved, and the surface is smooth, not being 

 ornamented as in the Lepidoptera. In the Tipiilidoi the 

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

 when they are immediately laid. 



The larvaB are footless, white, flesh}^, thin skinned, cylindrical 



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



higher families, as in the Tipulidm., a distinct head ; but they 



are often headless, as in the Muscidm, 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 



chrysalids of moths, with the limbs exposed, as in the Tipu- 



lidm ; 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, Avliich contracts 



slightly. It is then called the puparium, and is 



^^^ usually cylindrical and regularly rounded at each end 



V like the cocoon of moths. Those which have the 



Fig. 272. pupffi obtected, when aquatic and active, are provided 



with gill-like filaments permeated Avith trachea;. 



The semipupa stage of Diptera, corresponds generally with 

 that of the Hymenoptera and Lepidoptera. By an ingenious 

 device Dr. Fitch succeeded in observing in the living insect 

 the processes by which the larva of the willow Cecidomyia 

 (C salicis) turns to a pupa, and wliich is usually accomplished 

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

 change, at the anterior end of the larva the cutis or opake 

 inner skin becomes wholly broken up and dissolved into a 



