340 FORM AND STRUCTURE OF THE CELL [ch. 



embryological " studies from physiological and physical investiga- 

 tions, we tend ipso facto to regard each particular structure and 

 configuration as an attribute, or a particular "character," of this or 

 that particular organism. From this assumption we are easily led to 

 the framing of theories as to the ancestral history, the classificatory 

 position, the natural affinities of the several organisms : in fact, to 

 apply our embryological knowledge to the study of phylogeny. 

 When we find, as we are not long of finding, that our phylogenetic 

 hypotheses become complex and unwieldy, we are nevertheless 

 reluctant to admit that the whole method, with its fundamental 

 postulates, is at fault; and yet nothing short of this would seem 

 to be the case, in regard to the earher phases at least of embryonic 

 development. All the evidence at hand goes, as it seems to me, to 

 shew that embryological data, prior to and even long after the 

 epoch of segmentation, are essentially a subject for physiological and 

 physical investigation and have but the shghtest fink, if any, with 

 the problems of zoological classification. Comparative embryology 

 has its own facts to classify, and its own methods and principles of 

 classification. We may classify eggs according to the presence or 

 absence, the paucity or abundance, of their associated food-yolk, 

 the chromosomes according to their form and their number, the 

 segmentation according to its various "types" — radial, bilateral, 

 spiral, and so forth. But we have httle right to expect, and in 

 point of fact we shall very seldom and (as it were) only accidentally 

 find, that these embryological categories coincide with the lines of 

 "natural" or "phylogenetic" classification which have been arrived 

 at by the systematic zoologist. 



The efforts to explain "heredity" by help of "genes" and chromo- 

 somes, which have grown up in the hands of Morgan and others since 

 this book was first written, stand by themselves in a category which 

 is all their own and constitutes a science which is justified of 

 itself. To weigh or criticise these explanations would lie outside 

 my purpose, even were I fitted to attempt the task. When these 

 great discoveries began to be made, Bateson crossed the ocean 

 to see and hear for himself what Morgan and his pupils had to 

 shew and to tell. He came home convinced, and humbly marvelling. 

 And I leave this great subject on one side not because I doubt for a 

 moment the facts nor dispute the hypotheses nor decry the im- 



