302 G. E. COGHILL 



prevail in the development of the reflex mechanism of the trunk, 

 where the Rohon-Beard cells have their typical connection with 

 the skin and the motor cells have their terminals established 

 upon the muscles for a considerable time before they become 

 incorporated into a functional reflex arc and are, therefore, of 

 any value to the animal as regards behavior. From these facts 

 it appears, then, that the behavior-value of nervous processes, 

 if there be such in these nerve cells of early stages of develop- 

 ment, has no regulating influence in establishing the primary 

 plan of the integrating mechanism of the organism. WTiat this 

 regulating agency may be is one of the chief topics of interest 

 in my study, but it can be best discussed upon the basis of an 

 exhaustive anatomical and physiological analysis of the develop- 

 ment of the various elements of the central nervous system dur- 

 ing this early period. Such a study I already have well under 

 way. 



Since this paper was submitted for publication new evidence 

 of a 'general chemical sense' in the skin of animals has been pub- 

 lished by Crozier ('16) with particular reference to my sugges- 

 tion ('14, pp. 205-207) that the stimulating effect of substances 

 in solution may be accounted for by their destructive action upon 

 the epithelial cells. He concludes that there is "no ground for 

 Coghill's assumption that the cells of the germinative layer of 

 the epithelium of fishes and amphibians are exposed to the action 

 of the stimulating agent and thereby disrupted; and there is no 

 histological evidence of disruption." 



Without entering into further discussion or expression of 

 opinion I wish here merely to raise the following questions, which 

 seem to me to require settling before the main question at issue 

 can be regarded as closed: 



1. Since the skin of the invertebrate is very different anatomi- 

 cally from that of the vertebrate (the earthworm, for instance, 

 having sensory nerve cells in the skin with endings free on the 

 surface) may the reactions of the one be legitimately judged upon 

 the basis of the structure and function of the other? 



