EMBRYOLOGY 



41 



and into the beginning of the second day, by which time the ova have 

 migrated about one-fourth of the length of the oviduct, there occur 

 only three successive mitotic divisions, including the first segmentation 

 division, namely mitoses resulting in 2-cell, 4-cell, and 8-cell stages 

 while the ova are in transit in the oviduct. In making this statement 

 it is assumed that in the successive segmentations, the several cells 

 divide synchronously, which is not in conformity with the fact. These 

 three mitotic divisions are spaced at intervals of about 18 hours. 



TABLE 11 



Showing the distance of the ova from the fimbria at various ages. Based on table 



3, Huber ('15a) 



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



TABLE 12 

 Volume of ova and embryos. Condensed from table 4 Huber ('15a) 



In the next following division, the fourth, the ovum passes from the 

 oviduct to the uterine horn. Since the normal gestation period of the 

 non-lactating albino rat is only 21 to 23 days, this slow rate of increase 

 in volume and multiplication of cells during the first four days of de- 

 velopment is of especial interest and is very probably to be accounted 

 for by the inadequacy of the food supply of the ovum during its transit 

 through the oviduct. 



