28 G. CARL HUBER 



day after the beginning of insemination. During this period 

 the segmented ova migrate in the oviduct for a distance equaling 

 nearly half its length. The trustworthiness of the material, it 

 would seem to me, is shown by the fact that in the shorter time 

 stages the segmented ova are situated nearer the fimbriated 

 end, while in the longer time stages they approach the region 

 of the insertion of the oviduct into the uterine horn. This is 

 clearly shown in the reconstructions shown in figures 7 and 8. 

 A 3-cell stage was observed only twice: in one of eight ova 

 contained in the oviducts of rat Xo. 58 (2 days, 17 hours) and in 

 one of eleven ova found in the oviducts of rat Xo. 62 (2 days, 



Fig. 11 Two views of each of three models of 4-cell stages of the albino rat. 

 Rat No. 50, 3 days, 1 hour. X 200. A, 15, and C, gives a side view, A ', IV, and C 

 a vertical view, of each of the three models. 



22 hours). All the other ova found in these two animals were in 

 the 2-cell stage. In the two 3-cell stages noted, the undivided 

 blast omeres of each ovum presented a nucleus in mitosis; in one, 

 in the monaster phase, in one, in the diaster phase. The divi- 

 sion of the first two blastomeres, resulting in the 4-cell stage, it 

 would appear, occurs in the albino rat toward the end of the 

 third day. The material gathered at the beginning of the 

 fourth day after insemination presents throughout a 4-cell 

 stage. In D of figure 1 is shown reproduced one of the sections 

 of a series of six sections including one of the ova in the 3-cell 

 stage. Only one of the two cells resulting from the division of 

 one of the first two blastomeres is included in the section; the 

 cell in mitosis represents the undivided blastomere. 



