66 rUE AMKRICAX XATrUALlST [Vol. LV 



The armadillo egrg: like that of most mammals undergoes its 

 early development in the fallopian tube and is, therefore, cap- 

 able of reaching the blastocyst stage on its initial oxygen supply. 

 After this time, however, it must become attached to the uterine 

 wall for a further source of oxygen. For some reason in the 

 armadillo the reaction between the blastocyst and the uterine 

 wall is postponed, and the blastocyst is incapable ^of further de- 

 velopmental progress until this reaction is established and the 

 necessary supply of oxygen becomes available. In exactly the 

 same way the development of the blastoderm in the fish's egg 

 is oxporim-ntally retarded or stopped by reducing the available 

 oxyo-en supply and is again made to rosvinie its dovelopment by 

 snpplyiuo' oxyovn. In the case of the fish egg. the supply of 



lar to of tlic annadillo egg are only obtained as responses to 



ehaiigos in temperature and rate of oxidation. 



In tlie ai-madillo ege I also do not believe the retardation is 

 of the nature of a starvation phenomenon, since we see nothinar 

 of the kind in other forms. Temperature changes are ruled 

 out, since the temperature of the uterus is more or less constant. 

 The absence of oxygen necessary for the energetic process of 

 cell division, is, therefore, in all probability the arresting cause, 

 and tlio n'tai-datinu results in polyembryony. 



Til us Patters, in has found the developmental interruption to 

 exist, and lie has also shown the blastocyst to be disconnected 

 from the uterine wall and its necessary oxygen supply during 

 this time. However, he has furnished no data bearing on the 

 reason for the delay in uterine reaction and the consequent fail- 

 ure of immediate implantation of the blastocyst such as normally 

 occurs in other mammals. However, from what is known of the 

 dependence of uterine reactions on conditions in the ovary (Leo 

 Loeb,' Stoekard and Papanicolaou^ and others) it may very 

 probably be that some peculiarity in corpora lutea formation 

 is primarily responsible for the entire series of reactions leading 

 to polyembryony in the armadillo. 



The consideration of the armadillo egg up to this point has 

 taken account only of the external factors influencing its mode 

 of development. It must now be remembered as a fact of serious 



s Leo Loeb, Jour. Morph., Vol. 22, 1911. 



fi C. R. Stoekard and G. N. Papanicolaou, Am. Jour, of Anat., Vol. 22, 

 1917. 



