ON CARYOKINESIS. I/I 



the source of similarities in the latter must be sousfht 

 for in the community of their hereditary antecedents. 

 Hence, one way to place the doctrine of phyletic kin- 

 ship of two or more organisms upon a scientific basis, 

 would be to demonstrate the molecular or structural 

 affinities of their tissues, or what amounts to the same 

 thing, to demonstrate the molecular or structural affinity 

 of their germ-cells. The embryological phenomena of 

 a developing organism may be expressed in the terms 

 of protoplasmic metamorphosis. Two organisms at the 

 same stage of development would represent the same 

 stage of protoplasmic structure. The budding of a new 

 cell or the formation of a new organ would correspond 

 to the birth of a new phase in the course of the meta- 

 morphosis of the original protoplasm of the egg. 



To turn to our second problem. What is the cleavage 

 of the ovum ? What is accomplished by it ? Is it ''the 

 mere sundering of material which has no more reference 

 to the future organization of the embryo than the snow- 

 flakes bear to the size and shape of a future avalanche" ? 

 Or is it a ''histogenetic sundering" in which every step 

 in the process has a definite relation to the building up 

 of the future embryo ? These questions have been 

 raised from time to time and have been variously 

 answered. Upon this historical aspect of the question 

 it is not my purpose to enter at present. But that each 

 step of cleavage has some definite significance in relation 

 to the organization of the adult or of the larva, at least 

 in certain forms which have been most carefully studied, 

 there can be no question. Thus in a certain animal, it 

 has been observed that the nuclear substance of the 

 ovum is divided, during the first cleavage, in such a 



