EMBRYOLOGY 



31 



spermatogenesis : the second crop of spermatozoa is appearing, while 

 the first crop can be seen in the epididymis. Reduced number of chro- 

 mosomes 19. Allen (MS '15). 



b) Ovulation. According to the observations of Sobotta and 

 Burckhard, '10, ovulation is simultaneous in both ovaries — as 

 many as 13 egg cells have been found discharged. The ovum — 

 after fixation with Zenker's solution containing somewhat less 

 than the usual proportion of acetic acid — measured 60-65 n in 

 diameter with a nucleus about 25 n in diameter. The reduced 

 number of chromosomes is 16. The full number of chromosomes 

 32. The authors incorrectly assume that the common Albino is 

 a variety of Mus rattus. 



For the diameter of the living unsegmented egg Kirkham and 

 Burr ('13) give 79 n as a mean value. 



For the volume of the ovum see table 11. 



c) On the early stages of development we have the observations 

 of Huber ('15 a). His description is as follows: 



The material at hand permits the conclusion that in the albino rat 

 the segmenting ova pass from the oviduct to the uterine horn at the 

 end of the fourth day after the beginning of insemination, probably 

 in the 12-cell to 16-cell stage. With the beginning of the fifth day, as 

 will appear from further discussion, all of the ova are to be found in 

 the uterine horn. 



The following summary of the data gained by a study of the models 

 of oviducts containing ova in stages from the pronuclear to 12-cell to 



TABLE 10 

 Shouring the distance of the ova jrom the fimbria at various ages. Based on table 



S, Huber ('15a) 



RKCOBD NTTM- 

 BEE 



SIDE 

 RECON- 

 STRUCTED 



NUM- 

 BER OP 

 OVA 



106. 

 59. 

 62. 

 50. 

 51. 



R. 

 R. 

 L. 



R. 



L. 



1 day 



2 days 



2 days 22 hrs. 



3 days 1 hour 



4 davs 



Pronuclear 



2-cell 



2-cell 



4-cell 



12 to 16 cell 



0.25 

 0.63 

 0.84 

 0.90 

 1.00 



1 Not the entire length of oviduct was available for reconstruction. 



