40 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, 



