PARTHENOGENETIC CLEAVAGE OF THE ARMADILLO OVUM. 63 



one multicellular mass in which a. single cell is dividing mitotically, 

 but the spindle is of the size and character of a polar spindle and 

 lacks astral rays. Under the circumstances such a spindle would 

 probably be capable of interpretation as the first polar spindle 

 of an egg that had undergone degenerative fragmentation. 



Rubaschkin (1906), as the result of his studies of the guinea-pig 

 ovary, takes a decidedly negative stand, maintaining that all 

 mitotic figures occurring in ovarian ova during follicular atresia 

 are more or less distorted or otherwise abnormal maturation 

 mitoses, and in no sense the mitoses of embryonic cleavage. 

 Multinuclear and apparent multicellular conditions are inter- 

 preted by him as the result of degenerative changes brought about 

 by the conditions incident to follicular atresia. 



Athias (1908 and 1909) once more reviews the whole situation 

 and presents further data derived from the study of a number of 

 species of mammals. After summing up the evidence pro and 

 con he finds himself unable to reach a definite conclusion though 

 leaning decidedly to the negative point of view. Pending an 

 extensive program of investigation on the subject he prefers to 

 reserve judgment. 



My own investigations herewith presented were begun, as 

 stated, in 1909 and, as the reader will have discovered, support 

 the view that a limited amount of parthenogenetic cleavage 

 occurs but that development proceeds no farther than two or 

 three cell divisions. 



SUMMARY. 



The evidence derived from a study of large numbers of arma- 

 dillo 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 reorganiza- 

 tion as that seen in the armadillo. 



