Evidence from Rabbit Embryo 87 



no other means than the working of the same universal force but 

 guided by differently arranged extrinsic factors (chiefly yolk), and 

 by the interaction of the differently arranged intrinsic factors the 

 individual systems of the supposed form of energy. 



There is no mysterious determinant, id or engram which in the 

 one case causes the gut cavity to be formed by splitting, in the 

 other by invagination, in a third case, e.g., mammal, by infiltration 

 of fluid combined with splitting. 



The relationship of the special area of cell activity, which in 

 the vertebrate embryo gives rise to the growth in length (deutero- 

 genesis), to the primary area (protogenesis) again most probably is 

 capable of almost exact elucidation by mathematical means. In 

 my papers on the Rabbit there will be found figures in which 

 this relationship is roughly indicated, but they lack conviction, 

 because, if for no other reason, they lack mathematical proof. 



There is certainly no mammal, probably no animal, better 

 suited for the study of this particular point than the Rabbit, 

 because the Rabbit embryo develops from the first to the eighth 

 day entirely free from the influence of the uterus, and is almost 

 devoid of yolk, so that we are there dealing almost exclusively 

 with the living matter and its properties. The zona radiata is in 

 this case an important extrinsic factor, but this is wholly outside 

 the living embryo. 



If we get the relationship of the deuterogenetic to the proto- 

 genetic part of the organism clearly and mathematically defined, 

 should we have an explanation of the origin of the former? Or 

 should we have to fall back upon some supposed determinant, id 

 or engram ? 



Research might give it by showing how it is in reality present 

 from the first, though not apparent in the earlier stages (e.g., in 

 Rabbit 1-5 days though obvious during the 7th day). If so, then 

 there is no need for a special id or other determinant which induces 

 at the right moment the growth in length. 



A little reflection makes one realise that, with reference to those 

 animals in which an archenteron is produced by invagination or by 

 a process such as that characteristic of the Anura whereby a blasto- 

 pore and "blastopore lips" are formed, deuterogenesis is initiated 

 by the very fact of gastrulation, so that in those cases one can 



