60 HAYATO ARAI 



In all the foregoing cases semispaying was practiced before 

 puberty, but the final examination was made on the adult. 

 Consequently, these studies do not tell us what influence semi- 

 spaying has on the surviving ovary before puberty. 



As already mentioned, Bond holds that this compensatory 

 hypertrophy is probably due to an excessive growth of the ovarian 

 stroma. In my previous paper ('20) I stated that before ovula- 

 tion the weight of the ovary of the albino rat is most dependent 

 on the number of the large degenerated follicles and of those 

 nearly or completely mature, while after puberty the weight is 

 mainly influenced by the number of corpora lutea present. It 

 seemed desirable, therefore, to determine whether these facts 

 observed on the growth of the intact ovaries were applicable to 

 the hypertrophy of the surviving ovary, or whether, as Bond 

 holds, the excessive growth of the ovarian stroma is mainly 

 responsible. 



At the suggestion of Professor Donaldson, I undertook, there- 

 fore, the problem of determining the influence of semispaying 

 on the total number of ova in the surviving ovary, together with 

 a study of the cause of the compensatory hypertrophy. 



MATERIAL AND TECHNIQUE 



Albino rats twenty days old were chosen for operation, because 

 in my previous study ('20) it had been found that from twenty 

 until sixty or seventy days of age the number of ova is nearly 

 constant. If, therefore, the compensatory growth of the surviv- 

 ing ovary occurs during this period, we may be able to determine 

 whether the number of ova is responsible for it. For this special 

 point examination of the operated rat after puberty is not so 

 instructive, owing to the presence of the corpora lutea in the 

 ovary, which complicates the interpretation. 



For this study I used eight litters of albino rats. Each of 

 these contained at least four females. Three females in each 

 htter were operated on at twenty days of age, and the remaining 

 females used as the controls. These eight litters were divided 

 into two series. The rats belonging to series I were returned to 



