284 G. CARL HUBER 
persists through the later stages of segmentation, as for instance 
in the rabbit, the morula mass presents a spherical form. The 
transit of the ova through the oviducts is effected, very probably, 
through peristaltic action of the muscular coat, since only a 
relatively short portion is lined by ciliated epithelium. Whether 
or not there exists a rhythmic periodicity in the peristaltic action, 
it is impossible to state. The fairly regular rate of transit argues 
for the presence of some regulatory mechanism. The compact 
grouping often presented by a series of ova in transit through the 
oviduct, especially after reaching the portion with narrower 
lumen, suggests peristaltic action. 
The literature dealing with the segmentation stages of the 
albino rat is very meagre. Grosser figures what is presumably 
an 8-cell stage. His figure 27 is referred to only incidentally 
in the text, but in the accompanying legend it is stated that the 
figure shows “‘three ova of the white rat in process of segmenta- 
tion, with zona pellucida, in transit through oviduct, three and 
one-half days after insemination.”’ If I am right in interpret- 
ing these ova as in the 8-cell stage, this corresponds very closely 
to my own observation on rat No. 57, 3 days, 17 hours (figs. 
15-17). It is impossible to draw definite conclusions as to 
the segmentation of the ova of rats from the account of Melis- 
sinos. This observer while he states that his material includes 
the ova of mice and rats, and while considering segmentation 
mentions the ova of both forms, discusses them without dif- 
ferentiating between the two. His figures all refer to ova of 
the mouse. Selenka, Robinson, and Widakowich, who have 
contributed to our knowledge of the embryology of the albino 
rat, do not include the segmentation stages, to be found in the 
oviduct, in their account. 
The rate of segmentation and the time of transit through the 
oviduct, as given in the literature for certain other mammals 
is as follows: Sobotta has shown for the mouse that the 2-cell 
stage is reached about 24 hours after copulation, the ovum 
remaining in this stage to about the 48th hour. The 4-cell 
stage was observed at about 50 hours, the 8-cell stage at 60 hours, 
and the 16-cell stage at 72 hours ‘post coitum.’ The ova of the 
mouse pass into the uterine horn about 80 hours post coitum, 
