Implications of the Theories of Nerve Action 195 



the sensory and motor nerves of the corresponding segment. 

 If the head exercises a stronger influence upon the behavior 

 of the animal than any other segment, as in Nereis, for in- 

 stance, I believe it is due to the fact that in the oral end 

 more kinds of irritability are present and more peripheral 

 organs are differentiated (sense organs, mouth, etc.) than in 

 the other segments." 10 



Loeb has done good service in bringing together the evi- 

 dence for, and emphasizing the truth that, the segmental 

 make-up of the vertebrate head, so long and so ardently 

 studied by anatomists and embryologists, is as important a 

 matter for neural physiology as it is for morphology, and 

 that as a matter of fact the vertebrate spinal cord works 

 more or less on the segmental principle, and in this respect 

 falls into line with the central nerve axis of annelids and 

 arthropods. 



The first, or one of the first, investigators to recognize 

 this truth was Schrader, in his studies on the activities of 

 frogs whose brains had been wholly or partly removed. The 

 frequently quoted and later fully confirmed statement by 

 this investigator is of prime significance for the general 

 truth of what we might call fore-and-aft neural integration 

 in vertebrates. "The series of experiments we have given 

 teaches us that the central nervous system of the frog can be 

 divided into a series of sections, each of which is capable of 

 performing an independent function. It brings the central 

 nervous system of the frog into closer relation with the cen- 

 tral nervous system of the lower forms, which consist of a 

 series of distinct ganglia that are connected by commissures. 

 It speaks against the absolute monarchy of a single central 

 apparatus and against the existence of different kinds of 

 centers, and invites us to seek for the centralization in the 

 many-sided coupling of relatively independent stations." 



As statements much at variance from this concerning the 

 "central" function and power of different parts of the 



