AGE OF HUMAN EMBRYOS 415 



siderable accuracy by the cytological condition of the lutein 

 cells; however, all his specimens were from corpora lutea pre- 

 sumably a little older than the human ones mentioned above. 

 In a measure we may fill in the gap in the earlier stages from the 

 report by Sobotta^' on the development of the corpus luteum 

 in the mouse. He found in this study that during the first 24 

 hours after ovulation the cavity of the follicle fills with serous 

 fluid or blood, at the time the lutein cells become cut up into com- 

 partments by the formation of connective tissue septi. This 

 process continues during the following day or two, and finally 

 the central cavity is nearly obliterated, containing, however, a 

 central mucoid nucleus at the middle of the third day after 

 ovulation. 



The irregular summary from the several species is about as 

 follows: (1) In the mouse the central cavity of the corpus luteum 

 is obliterated about the middle of the third day after ovulation; 

 (2) it is obliterated in human specimens accompanying ova 

 about the size of those studied by Bryce and Teacher, and by 

 Peters; and (3), it is obliterated in the pig considerably before 

 the 25th day. It may also be noted that Corner states that the 

 corpus luteum of menstruation is of irregular shape in its develop- 

 ment, while that of pregnancy is uniform and even. He speaks 

 of the former as if the cells were arranged like a mob, and the 

 latter as if organized like an army. 



Finally, a few words regarding Fraenkel's studies, out of which 

 Triepel has made so much capital. According to Fraenkel, 

 Villemin in 39 operations found no freshly ruptured follicles in 

 the first two weeks after the menstrual period, but observed many 

 from 12 to 14 days before it. Fraenkel himself describes hemor- 

 rhagic follicles as follows: Very fresh, fresh, quite fresh and not 

 very fresh, showing that his average of 19 days after the last 

 menstrual period is not the average time of ovulation, but the 

 average of older corpora lutea in several stages of development. 

 From a study of Fraenkel's papers it may be seen quite clearly 

 that what he reports as fresh corpora lutea are by no means 



1^ Sobotta. 1896 Ueber die Bildung des corpus luteum bei der Maus. Archiv 

 fiir Mik. Anat., Bd. 47. 



