EMBRYOLOGICAL CRITERION OF HOMOLOGY. 1 03 



It is not to be supposed that the authors of these and similar 

 statements (which might be almost indefinitely multiplied) hold 

 an erroneous view of homology. The citations are given 

 merely to show how intimately the conception of homology 

 has become associated with the embryological data — how 

 prominent a place has been assigned to the embryological as 

 distinguished from the anatomical criterion for its determina- 

 tion. And, yet, it must be evident to any candid observer not 

 only that the embryological method is open to criticism but that 

 the whole fabric of morphology, so far as it rests upon embryo- 

 logical evidence, stands in urgent need of reconstruction. For 

 twenty years embryological research has been largely domi- 

 nated by the recapitulation theory ; and unquestionably this 

 theory has illuminated many dark places and has solved many 

 a perplexing problem that without its aid might have remained 

 a standing riddle to the pure anatomist. But while fully recog- 

 nizing the real and substantial fruits of that theory, we should 

 not close our eyes to the undeniable fact that it, like many 

 another fruitful theory, has been pushed beyond its legitimate 

 limits. It is largely to an overweening confidence in the value 

 of the embryological evidence that we owe the vast number of 

 the elaborate hypothetical phylogenies which confront the 

 modern student in such bewildering confusion. The inquiries of 

 such a student regarding the origin of any of the great primary 

 types of animals involve him in a labyrinth of speculation and 

 hypothesis in which he seeks in vain for conclusions of even 

 approximate certainty. Was the ancestral vertebrate most 

 nearly like an annelid, an arachnid, a crustacean, a nemertean, 

 or a tunicate } Who shall say whether annelids arose from 

 platodes, from medusae, from actinian-like forms, from "Tro- 

 chozoa," or from something else } It is not surprising that 

 morphology can give no certain answer to these questions, 

 for they are complex and difficult and must necessarily 

 be attacked by means of inference and hypothesis. It is, 

 however, a just ground of reproach to morphologists that 

 their science should be burdened with such a mass of 

 phylogenetic speculations and hypotheses, many of them mutu- 

 ally exclusive, in the absence of any well-defined standard 



