272 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 No. 58 (2 days, 17 hours) and in 
one of eleven ova found in the oviducts of rat No. 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, lhour. X 200. A, B, and C, gives aside view, A’, B’, and C’ 
a vertical view, of each of the three models. 
4 
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 
blastomeres 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. 
