PARTHENOGENETIC CLEAVAGE OF THE ARMADILLO OVUM. 6l 



found under similar conditions in the guinea-pig ovary. Not 

 having seen his preparations, but simply judging by his micro- 

 photographic illustrations, I am inclined to think that, since he 

 gets no intermediate or advanced cleavage stages, the cell 

 complexes he discusses are open to the interpretation just given 

 for similar phenomena in the armadillo, about whose synthetic 

 origin there appears to be no doubt. Parthenogenetic develop- 

 ment in all probability goes no farther in the armadillo than the 

 stages illustrated in the figures. That true parthenogenesis 

 begins and proceeds for a few steps seems assured, but it seems 

 highly improbable, a priori, that development could long con- 

 tinue in an environment so unfavorable as that afforded by 

 follicles in which atresia has made such progress as we have seen. 



DISCUSSION OF THE LITERATURE ON PARTHENOGENESIS IN 



MAMMALS. 



In 1900 Bonnet in an able paper entitled "Giebt es bei Wir- 

 beltieren Parthenogenesis?" reviewed all the literature dealing 

 with parthenogenesis in vertebrates and gave much space to the 

 question of parthenogenesis in mammals. He concluded that 

 there was no incontrovertible evidence of this mode of develop- 

 ment in any of the contributions dealing with the changes de- 

 scribed as occurring in ovarian ova during follicular atresia. 

 A considerable number of authors had described ovarian ova 

 containing centrally situated mitotic figures which they had 

 interpreted variously as cleavage spindles or as belated matura- 

 tion figures. Multicellular masses within zona pelucida were 

 described, in which some cells contained nuclei and others were 

 without nuclei. Some writers considered this condition as a 

 result of a degenerative fragmentation of nucleus and cytoplasm, 

 and others were convinced that the cell mass was the product 

 of parthenogenetic cleavage. Another class of writers called 

 attention to the existence of various kinds of more or less com- 

 plex ovarian dermoids, epithelioma and other teratoma, which 

 by some were interpreted as the end product of the partheno- 

 genetic development of ovarian ova. Judicially examining all 

 of the evidence before him Bonnet concludes that all of the 

 mitotic figures seen in ovarian ova are to be considered not as 



