POLYEMBRYONIC DEVELOPMENT IN TATUSIA 627 
These citations will suffice to indicate how widespread is the 
occurrence of polyovular follicles among mammals; but, although 
they have a distribution among widely separated forms, their 
occurrence in a given species seems to be rare. Thus O’Donoghue 
(12) found them but twice in forty-five individuals of Dasyurus; 
and Schron (’63) only twice in the ovaries of four hundred cats 
and but once in eighty dogs. The writer has examined in all 
probably more than fifty pairs of ovaries from the Texas arma- 
dillo without finding a single case. 
In the light of these data it is impossible to associate the occur- 
rence of polyovular follicles with the causation of polyembryonic 
development in mammals. The fact that Rosner has found a 
single armadillo with such follicles can have no greater impor- 
tance than have the similar sporadic cases in certain other mam- 
mals. The significant fact is, rather, that in the ovaries of fifty 
individuals belonging to a species which reproduces by specific 
polyembryony alone not a single case of polyovular follicles 
was found. 
It is well to emphasize the fact that the polyovular follicles do 
not lie at the basis of polyembryony, for to accept Rosner’s 
theory would be equivalent to a denial altogether of the phenom- 
enon of polyembryonic development in the Mammalia. A 
multiple gestation from ova which have accidentally become 
associated together during a part of the ovarian history, through 
the fusion of adjacent follicles, may have no more interest or 
significance than a similar gestation resulting from ova from 
uniovular follicles, but simultaneously ovulated, as occurs in 
many mammals that are normally multiparous. One cannot 
hope to throw much light on such fundamental biological problems 
as those of sex determination, the limits of hereditary control, 
and others, by the study of this type of development. It is only 
to those cases in which the several embryos of a multiple preg- 
nancy have taken their origin from a single fertilized egg that we 
must look for facts with which to elucidate these problems. 
It is not intended here to underestimate the biological impor- 
tance of polyovular follicles and of multiple gestations other 
than those of polyembryony; but rather to point out that these 
