IO2 H. H. NEWMAN. 



strictly external to ovum, among which one of the most probable 

 is in some way associated with the bilaterality of the uterus. A 

 discussion of this possibility would be foreign to the topic in hand 

 and must be postponed for subsequent treatment. 



The first five possible explanations will probably appear to the 

 reader to be without foundation and far-fetched. Every one, 

 however, has been offered by serious-minded biologists. The 

 majority of these explanations have already been shown to be 

 untenable, some require further refutation. It is one of the 

 purposes of this paper to remove the latter from further con- 

 sideration. There is a small amount of evidence in favor of the 

 sixth suggestion, but it is far from convincing. So it would ap- 

 pear that the stimulus to specific polyembryony must be looked 

 for in some external factors, the character of which we are not 

 prepared to discuss at present. This being the case a study of 

 the history of the female germ cells can furnish only negative 

 evidence on the main question at issue and would therefore lack 

 the inherent interest that usually attaches to positive results, 

 were it not that a considerable number of interesting, and, I 

 believe, important facts, apparently quite unrelated to the 

 phenomenon of polyembryony, have come to light. These facts 

 are therefore presented partly to pave the way for further cyto- 

 logical studies but principally because they appear to possess a 

 value quite independent of any of the general problems so far 

 suggested by studies of the armadillo. 



It is shown in this paper that the armadillo ovum bears a 

 remarkably close resemblance to that of Dasyurus, the native 

 marsupial cat of Tasmania, described by Hill ('10). In both 

 Dasyurus and Tatu the ovum, at maturity, exhibits an inverted 

 " telolecithal " condition. The genesis of this peculiar state of 

 affairs is traced through the growth period of the ovocyte and 

 incidentally a description of the parallel development of follicle, 

 ovocyte and germinal vesicle during this extensive period is pre- 

 sented in the belief that this phase of ovogenesis has been too 

 largely neglected by students of the maturation and fertilization 

 of the mammalian ovum. It will be noted also that the arma- 

 dillo ovocyte is especially favorable for the study of chromosomal 

 behavior during the maturation processes and that it is possible 



