OP WASHINGTON, VOLUME XIII, 1911 157 



short oviducts and very large ovaries; the other a uterus in 

 five or six coils, with long oviducts and smaller ovaries. Al- 

 though I have so far been unable to find differences between 

 either the flies or their eggs and maggots, I am not yet certain 

 of their identity. The difference in the length of the oviducts 

 and the size of the ovaries seems too great to explain by 

 descent of the eggs contained in the uterus, while there are 

 also quite important differences in the relative length of the 

 tubular glands and the spermathecal ducts. The whole mat- 

 ter serves to emphasize the necessity for much care and judg- 

 ment in the study of uterine characters. The delayed uterine 

 development might be thought to afford a clue to the age of 

 uterine specialization, indicating its comparatively recent ac- 

 quirement. But it is evident, as suggested by Pantel, that 

 the shortened condition of the uterus is essential to successful 

 coition and the free passage of the male fluid into the sper- 

 mathecae. Therefore full uterine development is delayed to 

 allow of copulation. 



In this connection the author points out a very serviceable 

 criterion, which is most conspicuous during dissection of the 

 forms with much uterine development, and which serves to 

 indicate such forms even in the newly issued flies before the 

 descent of the eggs and the elongation of the uterus have 

 begun. This is the fact that such forms have the uterus 

 abundantly supplied with masses of minute tracheae. These 

 positively indicate incubation of the eggs and development of 

 the maggots, and are often very troublesome by binding the 

 coils and other reproductive organs into a close tangle. 



Pantel calls attention to the idea advanced by Portchinski 

 that in Calliphora erythrocephala only one egg in each ovari- 

 ole develops. This is, I feel sure, a wholly mistaken idea. 

 It may happen in countries with an extremely short breeding 

 season, as in northern Russia perhaps, but in more southern 

 climes it can hardly be the case. All muscoid flies may be 

 easily divided into two grand categories on the character of 

 continuous or discontinuous development of ova in the ovari- 

 oles. Calliphora belongs in the latter category. One set of 

 ova develops at a time, the set being composed of the lowest 

 ovum in each ovariole. When these are fully formed, and the 

 fly has been fertilized, they are rapidly deposited in the case 

 of Calliphora, MHSCU^ Stomoxvs, etc. In the case of Sarco- 

 p/idQa, Metopia, etc., the set when fully formed descends 

 rapidly and practically at once into the uterus, where all de- 

 velop together. Practically always the eggs or maggots in 

 the uterus of these forms are all at the same stage of develop- 



