SEX RATIO OF THE ALBINO RAT 391 



table 3, include the four litters obtained when these males were 

 mated with semi-spayed females. If the records for these four 

 litters are excluded, the remaining thirteen litters are found to 

 contain a total of 65 individuals, which makes an average of five 

 young to each htter. This is doubtless a low average for the 

 litter of a normal albino rat; but it is very little lower than the 

 average size of the litters produced in the stock colony of The 

 Wistar Institute this past year. The small size of the litters 

 obtained in these experiments was probably due to some ex- 

 ternal factor, and not to the castration of the breeding males. 



The results obtained in these experiments indicate that, if 

 there is a dimorphism of the spermatozoa which is associated 

 with sex-determination, both female-producing and male-produc- 

 ing spermatozoa are developed in approximately equal numbers 

 in each testicle of every normal male. A similar conclusion was 

 recently drawn as the result of a series of investigations on the 

 influence of the spermatozoan on the sex ratio of the toad, Bufo 

 lentiginosus (King '11). 



The following conclusions seem warranted by the results 

 obtained in the series of experiments described in this paper. 

 They are valid, at present, only for the albino rat; whether they 

 can be extended to other mammals remains to be determined. 



1. Each ovary produces eggs that are capable of developing 

 into males and also eggs that can develop into females. 



2. Each testicle contains spermatozoa that are able to fer- 

 tilize the eggs from either ovary, and eggs thus fertilized develop 

 either into males or into females. 



3. The sex ratio is not altered in any way by semi-spaying or 

 by semi-castrating the breeding animals. It follows, therefore, 

 that: 



a. If sex is determined in the ovary, female-producing and male- 

 producing eggs are developed in approximately equal numbers in 

 each ovary of the normal female. 



5. If the male is responsible for sex, female-producing and male- 

 producing spermatozoa are developed in approximately equal 

 numbers in each testicle of the normal male. 



