1^0. 645] FECUNDITY IN THE GUINEA PIG 355 



When the two sisters were two months old, males were 

 introduced into the pens twice daily, but no signs of heat 

 were observed, and no matings occurred until these fe- 

 males were five months old. Similar results were obtained 

 with two other litters. Since my work was done Mr. 

 Warnock, a fellow student, has observed two females to 

 bear viable litters at the end of the third month. This 

 implies mating at the early age of one month. The pa- 

 ternal male was several months older, how^ever. 



The Cokpoea Lutea of Peegnancy 

 In order to study the correlation between corpora lutea 

 and implantations during the various stages of preg- 

 nancy, animals were mated and killed, from the seventh 

 day of gestation on, for each day up to and including the 

 fifteenth. From the fifteenth day to full term, animals 

 were killed every otlier day. 



When the guinea pigs were killed, the ovaries and 

 uteri were removed and placed in formalin for twenty- 

 four hours and the number of embryos in each horn of 

 the uterus recorded. The ovary corresponding to the 

 horn of the uterus having the larger number of concep- 

 tuses was arbitrarily chosen for use in determining what 

 relation might exist between the number of conceptuses 

 and the number of corpora lutea. Thus guinea pig No. 

 10 had two conceptuses in the right horn and one in the 

 left. The right ovary was embedded and cut serially into 

 thick sections. The left ovar>' was cut 7 micra thick 

 for the study of changes in the corpora lutea dtiring preg- 

 nancy. 



In a study of 14 embryos, Draper, '20, found 76 in the 

 left horn and 69 in the right, a ratio of 1 to 0.9. Of 98 

 embryos from 35 guinea pigs, I found 55 in the right horn 

 and 43 in the left, a ratio of 1 to 0.78. The average num- 

 ber of foetuses per pregnancy was three. 



Table II shows that there is a marked agreement be- 

 tween the number of corpora lutea in an ovaiy and the 

 number of implantations in the corresponding horn of 

 the uterus. Out of 34 ovaries examined, the number of 

 corpora lutea was the same as the number of embryos 



