286 G. CARL HUBER 
and 3-cell stages were obtained from the upper end of the uterine 
horn. The presence of 2-cell stages in the uterine horn has also 
been noted by Keibel, in Erinaceus europaeus, by Van Beneden 
in the bat, and by Hubrecht in the insectivor Tupaya javanica. 
Finally, it may be noted that according to the observations of 
Bischoff, the segmenting ovum of the dog occupies 8 to 10 days 
after insemination in transit through the oviduct. 
COMPLETION OF SEGMENTATION AND BLASTODERMIC 
VESICLE FORMATION 
The material covering the end stages of segmentation and the 
early stages of blastodermic vesicle formation is listed in table 5. 
TABLE 5 
ea NUM- 
IEABIEAO) ii AGE BER OF STAGE 
NUMBER OVA 
64 | 4days,14hrs. 5 | Early stage of blastodermic vesicle formation 
52 | 4 days, 15 hrs. 8 | Morula, beginning of segmentation cavity, early 
stage of blastodermic vesicle 
55 | 4 days, 16 hrs. Early stage of blastodermic vesicle 
| 
1 
68 4 days, 16 hrs. 4 Early stage of blastodermic vesicle 
53 > days | 7 | Early stage of blastodermic vesicle 
56 | © days 5 
Early stage of blastodermic vesicle 
Thus there are at hand 30 ova, showing late morula stages, 
the beginning of segmentation cavity formation and early 
stages of the blastodermic vesicle, falling in the latter half of 
the fifth day after the beginning of insemination. Jn all of 
the uteri from which this material was taken, the ova are spaced 
in the uterine horns about as in later stages of development; they 
lie free in the uterine lumen, are in the main ovoid in form, their 
long axis presenting no definite relation to the long axis of the 
uterine horn. In preparing this material for sectioning, 1t was 
the custom to cut an entire uterine horn into segments measur- 
ing about 1.0 em. to 1.5 em. in length. These segments were 
then embedded so as to admit cutting longitudinally and in a 
plane parallel to the plane of the mesometrium. Cut in this 
way, the majority of the ova were cut longitudinally or nearly 
so, others in an oblique plane, others again, crosswise. Since it 
