228 JOSE F. NONIDZZ. 



first period. 1 During the first five days after mating to the bar- 

 eyed male only hybrid females were produced; at the sixth day 

 normal females began to appear. Fortunately this fly was killed 

 at a critical moment, when fertilization of the eggs was about to 

 stop. Dissection showed that the ventral receptacle and one of 

 the spermathecse were empty, while a few active spermatozoa 

 could be seen moving along the duct of the other spermatheca. 



It is interesting to note that the number of normal females pro- 

 duced after crossing with the bar male is smaller than that of the 

 hybrid females. This peculiarity, which stands out clearly in all 

 the experiments, is due to the fact that the number of flies hatched 

 is higher when the parents belong to different mutant races. 



An important point in the mechanism of the discharge of the 

 sperm from the seminal receptacles is the influence exerted by the 

 egg on the spermatozoa. Whether or not the latter are attracted 

 by the egg is a point which could not be determined by the writer. 

 Although such an attraction, due to a chemotactic stimulus, is 

 possible, we must keep in mind that the same result may be at- 

 tained by reflexes set up when the egg enters the uterus, the re- 

 lease of the spermatozoa taking place upon dilatation of the ori- 

 fices leading to the seminal receptacles. The behavior of the 

 spermatozoa in sterile flies would throw some light on this prob- 

 lem, showing at least whether their discharge is related to the 

 entrance of an egg into the uterus. Such sterile flies are said to 

 be rather common in the inbred stocks of Drosophila mclano- 

 gaster (Hyde, '14) ; they do not lay eggs, probably on account of 

 the abnormal condition of their oviducts. If there is any relation 

 between the laying of eggs and the discharge of the spermatozoa, 

 such flies not laying any should keep the spermatozoa in their 

 receptacles ; otherwise the latter would appear empty after some 

 time. Some sterile flies which appeared in the bar-eyed stock 

 were given to me by Dr. Morgan, in the hope that this point could 

 be settled. Unfortunately such flies could not be mated, the 

 males giving up courtship after a short time. Very often a male 



1 The number of flies hatched must not be taken as a fair representation of 

 the number of eggs laid. Both males and females may die in relatively large 

 numbers during development, either as the result of intrinsic lethal factors or 

 of inappropriate environmental conditions. To this is added the sterility of 

 some eggs, especially during the first days following copulation. 



