362 H. H. Newman and J. T. Patterson. 



cleavage and come to a common point of attachment in the uterus; 

 subsequently the contiguous walls of the four blastocysts atrophy 

 and a single vesicular chorion is produced. 



Were Rosner's observations a record of the normal conditions 

 in the armadillo ovary the question of specific polyembryony 

 would assume an aspect entirely different from that suggested 

 by von Jhering, and we would need to seek no further for an expla- 

 nation of the observed conditions. The observation that all the 

 embryos in a litter are of the same sex was summarily dealt with 

 by Rosner who considered it as interesting but in no way connected 

 with the presence of a common chorion. Fortunately however 

 there is now every reason to believe that Rosner's material was 

 pathological or otherwise exceptional, for no subsequent investi- 

 gator has been able to find in the armadillo ovary conditions such 

 as he described. 



Cuenot, ('03), while engaged in the study of the problem of the 

 determination of sex, examined the ovaries of one pregnant and 

 of one virgin female of the species investigated by Rosner. In 

 the ovaries of the pregnant specimen there occurred only one 

 follicle of the pluriovular type and this contained only two small, 

 rather abnormal ova.(j3ut of 119 follicles in the ovaries of the 

 virgin female however three contained two or three eggs, but none 

 was found with the number requisite to give rise to the number 

 of young habitually born in a litter. 



Until quite recently no further progress was made toward the 

 solution of the problem. In 1909, however, there appeared almost 

 simultaneously and quite independently, two contributions to the 

 subject, one by Fernandez, ( J 09), on the Mulita (Tatu hybridum), 

 and the other a preliminary report by the present writers, ('09), 

 on the North American armadillo (T. no vemcinctum) . The iwo spe- 

 cies evidently agree very closely in many of the more fundamental 

 details of development but differ sufficiently to make it both inter- 

 esting and valuable, from the comparative standpoint, to have 

 the developmental history of both species worked out in the ful- 

 lest detail. 



Fernandez presents somewhat detailed descriptions of seven 

 rather early embryonic stages and enters upon a brief discussion 



