THE CKITEEIA OF HOMOLOGY IN THE PERIPHEKAL 

 NERVOUS SYSTEM. 



BY 



C. JUDSON IIEKRICK. 

 From the Anatomical Lahoratunj of the University of Chicago. 



Even a cursory survey of the literature of comparative neurology 

 reveals a confusion of usage among different authors who have 

 described the same organ under different names or ap]ilied the same 

 name to different organs. This confusion in some cases is so great 

 that it is necessary to add to the name of tho.^part the name of 

 the author whose usage is followed, in much .^^■i same way that 

 zoologists add the name of the authority after .he name of every 

 species. 



The confusion in many cases rests upon an imperfect knowledge 

 of the facts ; but in others it arises from differences in the inter- 

 pretation of commonly accepted anatomical and physiological data. 

 In so far as the latter is the case it suggests the necessity for an 

 analysis of the factors upon which homology rests and an attempt 

 on the part of working anatomists to come to an agreement as to the 

 relative value of these factors. 



It will, I think, be generally agreed that true homology always 

 rests, in the last analysis, upon genetic relationship of the parts 

 homologized. In the case of serial homology, or homodynamy, too, 

 I doubt not that the principles of homology of organs from species 

 to species will be found to apply with but small change in the mer- 

 istic comparison of organs from segment to segment in a metameric 

 body. This cardinal principle of homology requires that the parts 

 so homologized must have had a common origin phylogenetically, or 

 in the case of meristic organs have sprung from a common seg- 

 mental type. No functional or structural similarity, however close, 

 which has been brought about by convergence from diverse ancestral 

 'IHB Journal of Comi-arativb Neukolooy and PsycHOLOGy. — Vol. XIX, No. 2. 



