32 



ANATOMY 



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

 is presented to indicate rate of transit within the oviduct. The regu- 

 larity of the rate of transit as revealed in the summary may perhaps 

 speak for the trustworthiness of the age data as concerns my material. 



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

 duct while in the 2-cell stage (see table 10); transit through the last 

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

 curs, being relatively slow. It is hoped that these data, for the accuracy 

 of which I am dependent on reconstructions, may be of service to others 

 who may desire to collect segmentation stages of the albino rat. 



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 magnification 

 of 1000 diameters of ova presenting the stage in question. The respec- 

 tive volumes of these models were determined and the data reduced to 

 the actual volumes. 



TABLE 11 

 Volumes of ova and embryos. Based on table 4 Huber ('15 a) 



The uniformity of the figures giving the actual volume of the egg 

 mass, as determined by the weight of the water displaced by the models 

 of the respective ova reconstructed, leads me to feel that the errors com- 

 mitted in reconstruction were not serious. The last column of the 

 table, giving averages, is of interest since it shows a very slight increase 

 in the volume of the egg mass during segmentation and transit through 

 the oviduct. Following the pronuclear stage, which, as has been seen, 

 extends through a relatively long period and into the beginning of the 

 second day, by which time the ova have migrated about one-fourth of 



