Embryology. 1 1 7 



absolute. As in the case of sexual propagation, so 

 in that of karyokinesis, processes which are common 

 to all the Metazoa are not wholly without their fore- 

 shadowings in the Protozoa. And seeing how greatly 

 exalted is the office of egg-cells and even of tissue- 

 cells as compared with that of their supposed ancestry 

 in protozoal cells, it seems to me scarcely to be 

 wondered at if their specializations of function should 

 be associated with corresponding peculiarities of 

 structure a general fact which would in no way 

 militate against the doctrine of evolution. Could 

 we know the whole truth, we should probably find 

 that in order to endow the most primitive of egg-cells 

 with its powers of marshalling its products into a 

 living army of cell-battalions, such an egg-cell must 

 have been passed through a course of developmental 

 specialization of so elaborate a kind, that even the 

 complex processes of karyokinesis are but a very 

 inadequate expression thereof. 



Probably I have now said enough to show that, 

 remarkable and altogether exceptional as the pro- 

 perties of germ-cells of the multicellular organisms 

 unquestionably show themselves to be, yet when these 

 properties are traced back to their simplest beginnings 

 in the unicellular organisms, they may fairly be re- 

 garded as fundamentally identical with the properties 

 of living cells in general. Thus viewed, no line of real 

 demarcation can be drawn between growth and repro- 

 duction, even of the sexual kind. The one process is, 

 so to speak, physiologically continuous with the other ; 

 and hence, so far as the pre-embryonic stage of life- 

 history is concerned, the facts cannot fairly be regarded 

 as out of keeping with the theory of evolution. 



