280 G. CARL HUBER 
cavity, just distal to the opening of the oviduct, lying free in a 
slightly distended portion ef the lumen. This morula is of 
irregular discoidal form, presenting an appearance which sug- 
gests that it was fixed soon after it escaped from the oviduct. A 
fifth morula, of regular oval form, comprising very probably 18 
cells, all of which present resting nuclei, is lodged in a shallow 
pit of the uterine mucosa a little over 1 em. from the tubal open- 
ing. This portion of the uterine horn was not included in the 
reconstruction, the position of this morula is not, therefore, in- 
dicated in the figure. It is evident that this tube was fixed while 
the several morula masses were in transit from the oviduct to 
the uterine horn, which occurs, to judge from the material at 
my disposal, at the end of the fourth day after the beginning 
of insemination. The morula masses of the right tube are sit- 
uated in the oviduct just before its point of insertion into the 
uterine horn, in about the same relative position as are the 
three upper morula masses of the left side, as shown in the re- 
construction. They are of discoidal form, in close relation and 
appear to comprise, the one 12, the other two 14 to 16 cells. In 
B, C and D of figure 19 are reproduced sections of each of these 
three morula stages. The figures, however, are delusive in that 
the section for each passes through the greatest diameters of the 
respective morula. 
The material at hand permits the conclusion that in the 
albino rat the segmenting ova pass from the oviduct to the 
uterine horn at the end of the fourth day after the beginning 
of insemination, probably in the 12-cell to 16-cell stages. With 
the beginning of the fifth day, as will appear from further dis- 
cussion, all of the ova are to be found in the uterine horn. 
SUMMARY OF SEGMENTATION STAGES, RATE, AND VOLUME 
CHANGES 
The following summary of the data (table 3) gained by a study 
of the models of oviducts containing ova in stages from the pro- 
nuclear 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. The regularity of the rate of transit 
