222 EDWIN G. CONKLIN. 



has been, in the words of Owen, "correspondence in the relative 

 position and connexion of parts." Such correspondence has 

 been found to be much more fundamental than resemblances in 

 size, proportions, or details of structure. Similarly in germinal 

 organization it seems probable that the relative positions and 

 connections of organ bases are essentially alike in different mem- 

 bers of a phylum, though in other respects, they may vary 

 widely. A peculiar type of localization of organ bases is thor- 

 oughly characteristic of the ascidian egg and probably the same 

 thing is true of other phyla. If this be true, different phyla do 

 not approach one another more closely in the earliest stages of 

 germinal localization than in the cleavage or gastrular stages. 



ORIGIN AND EVOLUTION OF GERMINAL ORGANIZATION. 



The fact that there are various types of germinal localization 

 corresponding to different types of adult organization will be ex- 

 plained by most persons as due to the gradual " acceleration " of 

 development, or the shifting of adult characters back to earlier 

 and earlier stages of the ontogeny. It is but natural that those 

 whose attention is focused upon adult structures should regard 

 the adult as primary, the germ as secondary ; but it is surprising 

 that embryologists also have almost universally held a similar 

 view. Even students of cell-lineage and of the organization of 

 the egg have generally regarded this organization as secondary 

 and have explained it as the result of "precocious segregation," 

 or of the " reflection of larval or adult characters back upon the 



egg-" 



Such conclusions are not founded upon observation nor ex- 

 periment but upon preconceived notions as to the importance of 

 the adult and the extreme simplicity of the germ. The whole 

 life cycle is commonly viewed from the standpoint of the adult, 

 and all other stages are supposed to exist for the purpose of.lead- 

 ing up to a definite end stage. Similarly evolution is looked 

 upon as the transmutation of definite end stages into others by 

 direct modification of certain adult structures, which in some way 

 or other modify the germ and thus become inherited. 



But what is the evidence that, in either ontogeny or phylogeny, 

 the adult is primary and the germ secondary? What is the 



