379 



a precocious budding on the part of the embryonic vesicle may pave 

 the way for offering an explanation of polyembryony that will be 

 much more logical than that implied in the idea o| an early spon- 

 taneous blastotomy. 



Concerning the results obtained in the work on experimental 

 embryology, Conklin in his studies on Ascidians has pointed out the 

 pitfalls in the way of drawing definite conclusions regarding the 

 totipotence of separated blastomeres. He suggests that even an egg 

 which possesses a high degree of differentiation may have a great 

 capacity for regulation. 



It has been shown, in a paper in which the writer was as 

 collaborator^), that in many sets the four embryos of a litter very 

 closely resemble one another. Indeed in some sets the resemblance 

 is so striking that it amounts to almost complete identity among the 

 four embryos, or at least between the two individuals of a pair. 

 There are some sets, however, in which the resemblance is practically 

 wanting. In view of the fact that a considerable lack of uniformity 

 exists in the different foetuses, I believe that the facts of heredity 

 can be much more logically explained on the basis of budding. Cer- 

 tainly this is true with reference to the most striking fact brought 

 out in the study of heredity, viz., the close resemblance existing 

 between the individuals of a pair; for it has been definitely shown 

 that each primary bud produces two secondary buds, which are the 

 progenitors of the two embryos of a pair. For this reason we should 

 expect to find a close similarity between the individuals of a pair. 



It is true that a careful study of cleavage must be made before 

 the problems of heredity can be definitely settled; for it may be 

 maintained that a sort of '-physiological isolation" exists between the 

 products of the four blastomeres, from the time they aie first formed 

 until the embryos appear — and, furthermore, that this isolation 

 might defy the efforts of the student of embryology in his attempts 

 to obtain some morphological evidence of its existance in the early 

 stages. 



Coming now to the sporadic cases of gemelliparous development 

 in the human species which results in the production of identical 

 twins, I believe that these can be most easily explained by simply 

 assuming that each primary bud differentiates into an embryo, instead 



1) Newman and Patterson, Journal of Morphology, Vol. 22, No. 4. 



