630 J. T. PATTERSON 



of investigators, and in the earlier work on this armadillo the same 

 view was held. This idea undoubtedly has its inception in, and 

 has received most of its support from the results of certain ex- 

 perimental studies involving the mechanical or semi-mechanical 

 separation of early blastomeres. For it has been demonstrated 

 that an early isolated blastomere of the two-celled or four-celled 

 stage of the eggs of the echinoderm (Driesch '92), medusa 

 (Zoga '95-6), Amphioxus (Wilson '93), and teleost (Morgan '93) 

 may develop into a complete but small larva, and even in the egg 

 of the amphibian a blastomere of the two-celled stage, under 

 certain conditions (Schultze '95, Morgan '95, and Herlitzka '97) 

 may also develop into a complete organism. What then seemed 

 more logical then to conclude that in the case of polyembryonic 

 development the early blastomeres had in some way become 

 displaced or isolated, and that each cell thus separated formed 

 the center for a single individual. Moreover, this inference 

 seemed all the more plausible in the light of certain studies on 

 twins in the human species. Wilder ('04) in particular, in his 

 extensive paper on duplicate twins and double monsters, advo- 

 cates the theory that each member of a pair is the product of 

 one blastomere. 



The evidence that has been presented in the first part of this 

 paper makes it certain that polyembryonic development in the 

 armadillo cannot be explained on the basis of a spontaneous 

 blastotomy, in the sense that each embryo is the lineal descen- 

 dant of a single blastomere of the four-celled stage, and it causes 

 one to view with some doubt the conclusions of this same nature 

 that have been drawn by those who have worked on other poly- 

 embryonic forms. In this connection it should be kept in mind 

 that, although an equipotentiality seems well established for 

 the early blastomeres of the eggs of the echinoderms, medusa, 

 amphioxus, teleost, and others, yet there are many forms in 

 in which a blastomere does not have the power to develop into 

 a whole individual. Crampton ('96) on gasteropods, and Chabry 

 ('87) and Conklin ('05, '06) on ascidians have conclusively demon- 

 strated that a blastomere of the two-celled or four-celled stage 



