398 ROBERT W. HEGNER 



minute when compared with the enormous contents of the mature 

 egg, may become segregated at the posterior end of the egg and 

 there bring about the development of a greater volume of similar 

 substance, either by the division or budding of preexisting 

 particles, or from the yolk or cytoplasm under its influence. A 

 full discussion of this subject will reserved until the Keimbahn- 

 determinants of other animals have been described (p. 460). 



C. The Keimhahn in Compsilura concinnata Meig 



Compsilura is a tachinid fly, introduced into this country in 

 1906 for the purpose of destroying gypsy and brown-tail moths. 

 "Its eggs hatch in the uterus of the mother, and the tiny maggots 

 are deposited beneath the skin of the host caterpillar by means 

 of a sharp, curved 'larvipositor,' which is situated beneath 

 the abdomen" (Howard and Fiske, 1912, p. 219). The mag- 

 got is ready for pupation in about two weeks; the pupal period 

 is about one week; and the females require only about three or 

 four days after their emergence to become sexually mature. I 

 wish here to acknowledge my indebtedness to Dr. John N. 

 Summers of the Gipsy Moth Parasite Laboratory, jVIelrose High- 

 lands, Massachusetts, for an abundance of material. 



The internal reproductive organs of a sexually mature female 

 are shown in figure 6. Oocytes of various sizes are present 

 within the ovarian tubules (o.). At a point near the union of 

 the two oviducts (od) , the uterus is connected with two accessory 

 glands {a.g.), and three seminal receptacles {s.r.). The mature 

 eggs, which make their way down the oviduct and into the uterus, 

 are here fertilized. They then gradually move down the uterus 

 and are present to the number of about one hundred in a sexually 

 mature individual. All stages from the maturation of the egg 

 to the condition when the larva is ready to be deposited are passed 

 through within the uterus of the mother, and most of these may 

 be observed in a single specimen. Those eggs nearest the ovaries 

 are of course the youngest. An attempt to trace the origin of 

 the pole-disc granules in this species was unsuccessful, so only 

 two illustrations are presented here to show that in this species 



