212 The Unity of the Organism 



of the dividing egg, as in that of the ctcnophore, and under 

 some circumstances, the frog. Even before division begins, 

 this intimation of specific structure of the Qgg arrests our 

 attention. Our standpoint makes organization important 

 wherever found and of whatever grade. 



(«) Facts of Immediate Ohservation on Which the 



Conception Rests 



The truth is we now know that the undivided egg-cell 

 stage, in the individual life histories of animals so far as 

 they have been carefully studied, is already rather highly 

 organized and to a considerable extent specificaUy organ- 

 ized with reference to the kind of organism which the egg- 

 cell represents. Otherwise stated, we know that a thorough- 

 going account of the life history of any organism must in- 

 clude its structure and function in and before the undivided 

 egg-cell stage, as well as its structure and function after 

 cell-division begins. The science of germ-cell structure and 

 function previous to the egg-cell division is known to embry- 

 ologists as promorphology and prophysiology. 



The inductive evidence in support of the conceptions of 

 promorphology and prophysiology is altogether too volu- 

 minous and complicated to be fully presented in a work 

 like this ; but the matter is so important that the reader 

 must not be left in doubt about its conclusiveness. 



I call attention first to an aspect of the evidence which 

 though well known in a general way, is rarely if ever given 

 the consideration which in my opinion it merits. Reference 

 is made to the fact that many species of animals, even be- 

 longing to the same genus in numerous cases, have been 

 distinguished from one another in all their stages of de- 

 velopment down to the undivided egg-stage. Investigation 

 has gone so far in this direction as to make it probable that 

 ftU species whatever might be thus distinguished were thQ 



