40 



ANATOMY 



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

 16-cell stages in which latter stage transit to the uterine horn occurs, 

 is presented, to indicate rate of transit within the oviduct — table 11. 



It will be observed that the ova approach the uterine end of the ovi- 

 duct while in the 2-cell stage (see table 11); transit through the last 

 portion of the oviduct, where the greater part of the segmentation 

 occurs, being relatively slow. 



40000 



35000 



30000 



25000 



20000 



15000 



10000 



5000 



O 100 200 300 <-00 500 600 700 800 900 lOOO 



Age— days 



Chart 1 Showing the total number of ova in both ovaries of the albino rat 

 at different ages. 



In order to obtain the volume changes of the ova during transit 

 through the oviduct, beginning with the pronuclear and extending to 

 the 8-cell to 11-cell stages, reconstructions were made at a magnifica- 

 tion of 1000 diameters, of ova presenting the stage in question. The 

 respective volumes of these models were determined and the data re- 

 duced to the actual volumes- — table 12. 



The last column of table 12, giving averages, is of interest since it 

 shows a very slight increase in the volume of the egg mass during seg- 

 mentation and transit through the oviduct. Following the pronuclear 

 stage, which, as has been seen, extends through a relatively long period 



