364 DIPTERA. 



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

 ciently developed to be hatched, so that these animals are 

 viviparous. In the pupiparous Ilippobosca^, 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 ovicUict is a pair of glands 

 designed to secrete the gunun}- 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 Tipiilidoe the 

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

 when the}^ are immediately laid. 



The larvffi are footless, white, fleshy, thin skiuned, C3-lindrical 

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

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

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

 maggots. They live in mould, decajing 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- 

 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 

 slight^. It is then called the puparium, and is 

 usually cylindrical and regular^ rounded at each end 

 ^V^ like the cocoon of moths. Those which have the 

 Fig. 273. pupffi 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 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 which is usually accomplislied 

 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 



