No. 561] 



THE NINE-BA XDED ARMADILLO 



529 



logical causes of polyembryony? What factors deter- 

 mine the definite bilateral orientation of the embryos in 

 the vesicle, or what factors are responsible for pairing of 

 embryos? What light does the situation throw on the 

 problem of sex determination ? Does the condition give 

 us any fulcrum on the problem of predetermination and 

 epigenesis? What are the modes of inheritance peculiar 

 to polyembryony? Does the polyembryonic situation 

 offer any new facts bearing on the general problems of 

 genetics ? These problems will be discussed in the order 

 given. 



The Causes of Polyembryoxy 

 In a previous paper (Newman, '12) were listed a series 

 of seven possible explanations of polyembryony, nearly 

 all of which assumed some abnormality in ovogenesis, 

 maturation or fertilization. The discovery that all of 

 these processes are normal in the armadillo served to 

 eliminate all but the last suggestion, which was to the 

 effect " that the cause of specific polyembryony may Lie 



of the most probable is in some way associated with the 

 bilaterality of the uterus." At that time no discussion 

 of that possibility was attempted. The discovery of a 

 specific parasite within the armadillo egg, together with 

 a consideration of certain unpublished data presented 

 orally by Patterson, leads me to hazard the following 

 hypothesis. 



A careful examination of many ovaries and many 

 thousands of ovocytes has revealed the universal pres- 

 ence of what I consider to be a protozoan parasite in the 

 egg cytoplasm. This parasite is a large body as com- 

 pared with the size of the host cell and must have a 

 deleterious effect on the egg, probably weakening it or 

 lowering its vitality. Such a depressed egg, in which the 

 parasite has grown and multiplied, develops into a vesicle 

 of some size before the effects of a lowered vitality be- 



