59s 



THE AMEBIC, 



'ST [Vol.XLVI 



either after having suckled her young or after having lost 

 them. She will then ordinarily copulate within a few 

 days after having been put with the male. The following 

 representative table of ten consecutive cases emphasizes 

 this point. 



table I 



Out of the above ten cases in which the females had not 

 suckled young for some time, and then were put with 

 males, nine cases of copulation evidently resulted early, 

 since the young were born within an interval only a little 

 greater than the normal period of gestation following a 

 rest (that is, 20 days) (6). 



The eighth case, although unusual, has been further 

 accentuated by more recent data which show that the 

 female may remain with the male for long periods with- 

 out becoming pregnant. This is not conclusive evidence, 

 however, that an unsuccessful copulation may not have 

 taken place within that time. In fact, I have found that 

 in a surprising number of cases copulation does not result 

 in fertility. As an example of this may be cited 25 con- 

 secutive cases which I observed, 10, or 36 per cent., of 

 which resulted in infertilty. 



In interpreting this sterility I was at first inclined to 

 believe that it was due entirely to the females, but since 

 then 1 have found males in many cases unproductive. 

 Some of these were useless for breeding because they 

 were practically unresponsive, rarely if ever copulating ; 

 others, although among the most active males, proved un- 

 fertile. The following example may be given to show 

 such a case. 



