POLYEMBRYONIC DEVELOPMENT IN TATUSIA 567 



which the egg came; the fifth, the age of the mother; the sixth, 

 the number of the figure, in case the specimen is illustrated in 

 the paper; the seventh, remarks. Unless otherwise stated, under 

 remarks, the vesicle was taken from the right to left horizontal 

 groove of the uterine cavity. In most instances differences in 

 size indicate differences in the degree of differentiation among the 

 several blastocysts, although there is some variation in vesicles 

 showing corresponding differentiations. 



The table brings out several interesting points, and to those that 

 will not be specifically treated in subsequent sections we must 

 direct a few remarks. 



In twenty^nine of the thirty-two cases listed the ovary from 

 which the egg came was determined; and the record shows that 

 fourteen were derived from the right ovary and fifteen from the 

 left, thus indicating that there is no tendency for one ovary to 

 function more frequently than the other. In two 'of the remaining 

 cases I failed to make a record on this point, but in the third (No. 

 297) both ovaries were enlarged. This would indicate that occa- 

 sionally the two ovaries function simultaneously, although in this 

 particular case I was not able to find a second egg. There is of 

 course the possibility that the one ovary gave off an egg which 

 failed to become implanted, and that a second ovulation, involving 

 the other ovary, followed immediately. 



It was stated above that the 'old' females, that is females which 

 have previously borne young, breed first, and that the second year 

 virgin females come on later. The table brings these facts out 

 clearly. Thus, of the eighteen cases with complete records, which 

 were taken in October, fourteen (Nos. 230, 287, 288, 291, 292, 295, 

 297, 300, 304, 305, 309, 320, 325, 326) were from old females, while 

 only three were from virgin females, that is females that had never 

 before borne young. Of the eleven cases involving second year 

 females, eight vesicles (Nos. 243, 244, 245, 251, 258, 259, 261, 335) 

 were taken between November first and eighth; while two of the 

 remaining three were secured late in the month of October, both 

 on the 26th (Nos. 311, 315). Finally, of the three vesicles 

 obtained from the first year females, that is females that had 

 been born during the previous winter or spring, two were taken 



