224 J SE F - NONIDEZ. 



in the first four days, the others laying eggs continuously dur- 

 ing the seven days. The flies belonged to the same generation, 

 were isolated on the same day, the isolation period prior to mating 

 being three days. The number of eggs layed was 470, 336, 335, 

 238, 221, 206, 200 and 117. In the female which laid 470 eggs 

 only a few spermatozoa could be detected in the ventral recep- 

 tacle. In the female which laid the smallest number of eggs 

 (117) about two thirds of the ventral receptacle was filled with 

 spermatozoa. The amount of sperm present in the ventral recep- 

 tacle of the other flies could not be estimated accurately, but de- 

 creased noticeably as the number of eggs laid increased. Inspec- 

 tion of the spermathecse in all of the eight flies showed the 

 presence of abundant spermatozoa closely packed; no sperma- 

 tozoa were detected along the ducts of these organs. Additional 

 dissections of flies killed from twelve to fourteen days after fer- 

 tilized proved in all cases the correctness of this view. 



As the ventral receptacle begins to empty its spermatozoa it 

 may be seen that the latter are turning around so as to have their 

 heads directed toward the opening of the receptacle into the 

 uterus. This rotation was very conspicuous in most of the flies 

 dissected, the spermatozoa being scattered in the proximal por- 

 tion of the receptacle without definite orientation. 



The bulk of the sperm does not go to the immediate vicinity of 

 the opening of the ventral receptacle into the uterus when their 

 discharge begins, but remains in the free end of the receptacle, 

 only a few traversing the empty space which separates the latter 

 from the orifice, to be poured into the anterior portion of the 

 uterus. The inspection of the initial portion of the receptacle 

 showed a few spermatozoa swimming towards the uterus when 

 this contains an egg ; the portion of the receptacle near the opening 

 is so narrow that only a few spermatozoa can pass at a time. 



Owing to the position of the micropyle in the egg within the 

 uterus it was thought that the spermatozoa stored in the sperma- 

 thecse might be unable to fertilize any eggs, since the orifices lead- 

 ing to these organs are placed in the dorsal wall of the uterus and 

 the appendages of the egg come to lie between these orifices and 

 the micropyle. Some experiments were carried out in order to 

 ascertain this important point. Ten flies were simultaneously 



