384 G. CARL HUBER 
not to be explained on the supposition of superfecundation or 
superfoetation. The record for this rat does not show insemi- 
nation on successive days. At The Wistar Institute, after all 
of the supposedly successful matings of albino rats, the females 
rats are caged apart from the males. The smaller egg-cylinder, 
though appreciably smaller, is in stage of development separated 
from the other by a time interval of perhaps less than 24 hours. 
It presents a stage of development which is comparable to C 
of figure 27 (8 days) and except for size, to the one figured in 
figure 29 (8 days, 17 hours) of Part I. It is believed that in this 
case both ova were seminated at about the same time, and pro- 
ceeded through normal segmentation and that on reaching the 
lumen of the uterus during the fifth day they became lodged in 
close proximity in the same mucosal fold. With the development 
of the decidual crypts, both became enclosed within the same 
erypt, at perhaps slightly different levels. In further develop- 
ment one blastodermic vesicle dominated the other and from 
about the seventh day on, one developed and differentiated 
more rapidly than the other. Had development continued, two 
distinct embryos, with separate amniotic cavities, attached to 
the same placenta, would have been formed, with one embryo 
large and more fully developed than the other. From mere 
difference in size and of development of embryos in the same 
litter it is not warranted to postulate superfecundation nor super- 
foetation. I am of the opinion that usually when two morula 
masses are lodged in close pres: in the same mucosal fold, 
one or the other degenerates (fig. 2, A) and that the normal 
development of both, as in the preparation shown in figure 10, 
is of very rare occurrence. 
CONCLUSIONS 
A study of the abnormal or pathologic ova met with in the ex- 
tended series of preparations covering the first ten days of the 
development of the albino rat, enables grouping them in two 
main classes: 
a. Such in which all of the ova of a given rat show, or are 
associated with, abnormal development. 
