The evidence derived from a study of large numbers of armadillo ovaries demonstrates, I believe, that parthenogenetic cleavage takes place in atretic follicles of this species of mammal. Whether cleavage is preceded by maturation is not clear, but I am inclined to believe that no polar bodies are extruded in those ovocytes that are destined to undergo cleavage. There is strong reason to believe that the abstriction of the deutoplasmic material in these ovarian ova is equivalent to one of the steps in normal development, for a similar process occurs in the development of several marsupials, the ovogenesis of which shows the same history of deutoplasm formation and reorganization as that seen in the armadillo. There is no evidence that cleavage proceeds beyond the eight-cell stage, and even at that period there are many signs of advancing degenerative processes. It seems certain, therefore, that, in the armadillo at least, no complex tissue masses such as ovarian teratoma or epitheliomata result from a continuation of the process of parthenogenetic cleavage.