144 MEDICAL ENTOMOLOGY 



seen in bulk, and contains a large number of granules in suspension. 

 Some of these are fatty, but the majority appear to be of an albuminous 

 nature. The fluid is used, exactly as in mammals, for the nourishment 

 of the young. It is not, however, entirely absorbed by the larva, 

 but is retained in considerable quantity in the stomach, to serve for 

 the nourishment of the larva after it has left the body of the 

 parent. 



The normal physiology of reproduction may be summarized as follows. 

 The lowest follicles of the ovary produce eggs in turn, and as each is 

 fertilized it passes down into the uterus. It has been 

 shown by Roubaud that, if fertilization does not occur, 

 the egg is retained in its position in the ovarian sheath, while the eggs 

 which should be produced after it continue their growth up to a certain 

 point. Fertilization, in fact, determines the passage of the egg to the 

 uterus, but not the maturation of the eggs contained in the ovarian tubes. 

 When it has passed into the uterus after fertilization the egg hatches, and 

 a young larva emerges. The larva is free in the cavity of the uterus, but 

 the walls of the latter, by virtue of their muscular tissue, contract around 

 it, accommodating the size of the cavity to the size of the larva as it grows. 

 The mouth of the larva is situated at the ' teat ' formed by the entry of 

 the ducts of the milk glands into the uterus, and the larva, by a special 

 apparatus, sucks the fluid from the glands into its stomach, which is 

 always full under normal conditions. The posterior end of the larva is 

 placed at the vulva, the muscles surrounding which are so arranged as to 

 enable the cavity to be placed in communication with the external air, in 

 order to allow the larva to breathe through the stigmata at its poste- 

 rior end. The stay of the larva in the uterus is about ten to eleven days. 

 When mature it is expelled by the contraction of the muscular coat of 

 the uterus ; its stomach at the time of birth is still full of the milk derived 

 from the mother. It then crawls away to pupate. 



The reproductive process in Glossina has been shown by Roubaud to 

 be easily influenced by changes in the environment. As these have a 

 direct bearing on the bionomics of the fly they will be discussed in that 

 connection. 



Whereas the pupiparous habit in Glossina is markedly at variance with 

 the method of reproduction in the rest of the Muscidae, in the 

 Pupipara the habit is the rule, and forms the distin- 

 guishing character of the family. The subject is of 

 great interest, and even before the practical importance of it was 

 recognized it had already attracted a good deal of attention from 



