June 22, 1917] 



SCIENCE 



623 



omy of parts, then, is one of the most strik- 

 ing aspects of the neuromuscular organiza- 

 tion of the sea anemones and is strong 

 evidence in favor of the absence of a central- 

 ized nervous organ in these animals. The 

 same conclusion can be drawn from certain 

 aspects of the feeding habits of sea ane- 

 mones. If one of these animals is persist- 

 ently but slowly fed by the tentacles on one 

 side of its mouth, it will sooner or later 

 cease to take food by these tentacles, though 

 the muscles of the tentacles are in no sense 

 fatigued. If food is now applied to the 

 tentacles on the opposite side of the mouth, 

 feeding will recommence almost as though 

 the animal had not been fed previously. 

 Thus the change of response induced on 

 one side of the mouth has had little or no 

 effect on the other, a condition referable to 

 the absence of a central nervous organ. It 

 is thus evident how different the organiza- 

 tion and the responses of an animal without 

 a central nervous organ are as compared 

 with those of forms possessing such an or- 

 gan. 



Sense organs and muscles may therefore 

 be regarded as two elements more primitive 

 than the central nervous organs in the evo- 

 lution of the neuromuscular mechanism. 

 What is the source of these two parts 1 Did 

 they arise together, twins at a single birth, 

 or is one the older, and, if so, which? 

 Kleinenberg in his theory of the neuromus- 

 cular cell, and the Hertwigs in their ac- 

 count of the nervous system of sea ane- 

 mones, were both led to declare in favor of 

 the simultaneous and dependent origin of 

 nerve and muscle. Claus believed that 

 these two elements arose independently and 

 came together secondarily, a view subse- 

 quently espoused by Chun. When, how- 

 ever, animals more primitive than sea ane- 

 mones, such, for instance, as sponges, are 

 studied, a different solution to the problem 

 from those just suggested is obtained. 



These lowly forms as mature animals pos- 

 sess no powers of locomotion whatever and 

 the few movements that their bodies exhibit 

 are carried out with the utmost delibera- 

 tion and slowness. They can very slightly 

 and always with great slowness bend and 

 unbend their bodies as a whole, and they 

 can close and open the numerous inlets 

 and the few outlets by which the spaces 

 within their substance are set into com- 

 munication with the surrounding water. 

 All these movements are carried out by a 

 very simple form of muscular tissue and 

 so far as concerns the study of their bodies, 

 both anatomical and physiological, there is 

 no evidence whatever of the presence of 

 sense organs or other forms of nervous tis- 

 sue. It therefore seems quite certain that 

 in sponges we have primitive animals pos- 

 sessed of muscle but devoid of nerve even in 

 the form of sense organs, and we may there- 

 fore conclude that, between muscle and 

 sense organs, the muscle is of more ancient 

 origin and marks the beginnings of that 

 series of functionally related parts that cul- 

 minates in the central nervous systems of 

 the higher animals. 



These views as to the steps in the evolu- 

 tion of the nervous system, as to the sources 

 of our nervous structures and activities, 

 have already found expression. They carry 

 with them, however, certain implications 

 concerning the manner in which we should 

 frame our hypotheses as to the springs of 

 nervous action, implications that have not 

 been so generally appreciated. In the early 

 part of this address I sketched the com- 

 monly accepted view of the organization of 

 nerve and muscle in the higher animals. 

 From the standpoint of human interests the 

 sense organ is the avenue through which we 

 gather in the course of our lives that enor- 

 mous body of information concerning our 

 surroundings. By smell, taste and touch 

 we gain a knowledge of the more elemen- 



