191 1.] THE PRmiTIVE NERVOUS SYSTEM. 225 



be brought into coordinated action from a single point on its sur- 

 face and, secondly, as the storehouse for the nervous experience of 

 the individual and the seat of those remarkable activities that we 

 recognize in the conscious states of the higher animals. Thus nerve 

 and muscle did not develop independently, as claimed by Claus and 

 Chun, or simultaneously, as maintained by Kleinenberg and the Hert- 

 wigs, but muscle appeared first as independent effectors and nerve 

 developed secondarily in conjunction with such muscles, first as a 

 means of quickly setting them in action and, secondly, as a seat of 

 intelligence. 



When we survey the whole range of metazoan development, we 

 cannot but be struck with the remarkable history of the neuro- 

 muscular mechanism. The earliest metazoans were doubtless little 

 more than colonies of protozoan cells concerned with the common 

 functions of feeding and reproduction and conforming more or less 

 to Haeckel's hypothetical gastrsea. To these early functions of this 

 primitive metazoan were added colonial reactions in that a system 

 of independent efifectors, more or less such as we see in the muscu- 

 lature of the modern sponge, was differentiated. As a means of 

 bringing this musculature into more effective response, nervous ele- 

 ments developed in close proximity to the effectors. With the growth 

 of the musculature and the nervous system in volume and with the 

 consequent increase of metabolism, came the development of the cir- 

 culatory system and its dependencies, the respiratory and the excre- 

 tory organs. Thus the relatively simple body of the primitive meta- 

 zoan became gradually converted into that of the more complex type. 

 In all these changes no system of organs has done so much to unify 

 the metozoan body as the nervous system. If a sponge may be out- 

 lined as a metazoan whose organization concentrates on feeding and 

 reproduction, a human being may be described as one whose organi- 

 zation centers around nervous action. In such an organism the 

 nervous system is supreme ; and the rest of the body may be said 

 to do little more than aft'ord a favorable environment for this system ; 

 and yet, if the preceding account is correct, this most important 

 system originated som.ewhat late in the history of the metazoa and as 

 a relatively insignificant organ for the discharge of muscular activity. 



Harvard University, 

 April 20, 191 1. 



