No. 645] FECUNDITY IN THE GUINEA PICx 357 



absorbed or that an ovum degenerated before implanta- 

 tion, or that it failed of fertilization. 



As shown by Meyer, '17 and '19, and Stockard and Pa- 

 panicolaou, '18, absorption is not uncommon in the uteri 

 in guinea pigs. In this series, three embryos which were 

 clear-cut cases of absorption were found upon examina- 

 tion of the uteri after their removal. In No. 12, which 

 was killed forty-five days after copulation, two normal 

 embryos were found in the left horn, but in the right horn 

 there was nothing but a small mass which had undergone 

 almost complete absorption. 



According to Stockard and Papanicolaou, '18, embn^os 

 eight or ten days old may be detected by " carefully feel- 

 ing the uterus through the body wall of the mother." 

 They report a case as follows : 



A normally developed embryo 19 mm. crown rump length is sliown 



that of a ten-day specimen, while the normal individual was a typi- 

 cal 20-day specimen. This case was detected by external examination 



the phenomenon. 



Although I used the method of Papanicolaou and Stock- 

 ard in palpating guinea pigs, in no instance was I able 

 to determine the number of embryos with certainty under 

 fifteen days. Because of this fact, I found it necessary to 

 sacrifice the animals in order to determine the number of 

 implantations before this period. 



Guinea pig No. 35 and guinea pig No. 34 were killed 

 seven and eight days after conception, respectively, and 

 the uteri removed. Careful palpation of the removed 

 uteri failed to reveal the number of conceptuses. The 

 uteri were then opened, but in order to determine the 

 number of itiiplantations ])rc'soiit it was necessary to em- 

 bryos in tlu"'utcni^ l.> pnlpatioii tliroii-li tlio al..loini!ia I 

 wall on the eighth to tentii day of pivgiiaiicy. This sk.'i)- 

 tieism seems warranted, further, by the measurements of 



