SEX RATIO OP THE ALBINO RAT 389 



inbreeding experiments, and it is well known that inbreeding 

 causes a marked decrease in the number of offspring. A normal 

 sister of two of the semi-spayed rats was mated four times to a 

 normal male. She had a total of 24 young, of which fourteen 

 were males and ten were females. The average number of indi- 

 viduals to a litter in this instance was six. One of the females 

 operated upon by Doncaster and Marshall gave birth to a litter 

 of seven young; but none of the semi-spayed rats used in these 

 experiments ever had a litter containing more than six individuals. 

 It seems probable, therefore, from the data shown in table 2, 

 that semi-spaying causes a decrease in the average size of the 

 litters, although it has no appreciable effect on the sex ratio, and 

 apparently does not decrease the number of litters a female can 

 produce. 



Two of the semi-spayed females used in these investigations 

 died from pneumonia; the other two were etherized when it 

 became evident that they were out of condition and would not 

 breed again. An autopsy was made in each instance, and in no 

 case was there any ovarian tissue on the side of the body that had 

 been operated upon. The remaining ovary appeard normal in 

 every female, and there was no marked increase in its size to 

 compensate for the loss of the other ovary, as Doncaster and Mar- 

 shall found to be the case in each of the two rats upon which 

 they had operated. As these investigators operated upon adult 

 rats and killed them about two months after the operation, it 

 seems probable that the noticeable increase in the size of the re- 

 maining ovary must have been due to some pathological condi- 

 tion, and not to a normal 'compensatory hypertrophy.' There 

 is a considerable variation in the size of the ovaries of the same 

 rat, as well as in those of different rats; and it is not improbable 

 that the same ovary varies in size at different times. A series 

 of careful measurements would have to be made of a number of 

 ovaries, removed from females at different times in the month 

 and at different seasons of the year, in order to obtain proper 

 standards by which to measure any apparent deviation from the 

 normal size. 



