194< The Unity of the Organism 



tube depends upon organs which are located in the forward 

 end of the body and whose sensory nerves go to the supra- 

 esophageal ganglion." 9 



One office of the Nereis brain is, therefore, to make a 

 great complex of activities normal, or "of the same nature" 

 as sane activities in "rational human beings." Not the ac- 

 tivities themselves but their normality are dependent on the 

 brain. This distinction is undoubtedly general, but it is 

 definite so far as it goes. Beyond question to the student 

 who should compare the movements of the normal and the 

 brainless Nereis with sufficient care, the distinction between 

 the two would be as positive, as indubitable, and as definable 

 as that between almost any two complexes of organic phe- 

 nomena. The unsatisfactoriness of the distinction is not its 

 vagueness but its generalness. It is sufficiently definite 

 though not sufficiently analytic. 



Just what the brain does to normalize the activities ; in 

 other words, how the change of character of the worm's 

 behavior its "restlessness" and general insane-like conduct 

 results from the absence of the brain, is not known. Loeb 

 makes a suggestion toward an explanation, but recognizes 

 what he offers as nothing more than a suggestion ; so to go 

 into it is not worth our while. 



But there is an obvious usefulness of the ganglia and 

 whole neural chain in such animals aside from the general 

 one of normalizing behavior. It serves as a common con- 

 ducting and relay system between the peripheral sense or- 

 gans and locomotor muscles. Loeb's statement of the matter 

 is concise and may be adequate: "The central nervous sys- 

 tem does not control response to stimulation; it merely 

 serves as a conductor from the point of stimulation to the 

 muscle through which weaker stimuli may pass, and pass 

 more rapidly than would be possible if the muscle were stim- 

 ulated directly. 



"In the Annelids each ganglion is a relay station for 



