88 COMPARATIVE PHYSIOLOGY OF THE BRAIN 



practically destroyed by dividing the ganglion chain, 

 for the deep incisions between the single segments 

 prevent the entire cutaneous muscle layer from being 

 stretched equally. The structure of the ventral nerve- 

 cord in Nereis is so similar to that of Lumbricus that 

 we should not be justified in seeking in it for the 

 conditions which cause difference of behaviour. In 

 earthworms, Maxwell succeeded in confirming Fried- 

 lander's observation. I obtained similar, although 

 not as marked, results on leeches (2). 



If an earthworm be divided, the posterior, brainless 

 piece continues to perform progressive movements. 

 This fact confirms the opinion that the brain has no 

 controlling part in progressive movements. 



4. The question now arises, Are the remaining char- 

 acteristic functions of the earthworm brain-functions 

 or segmental functions ? If we place Lumbricus fosti- 

 dus in a transparent closed vessel, the animals appear 

 to be positively stereotropic. As soon as they reach 

 an angle in the aquarium, they remain there, crawling 

 along where the glass can touch them on two sides. 

 They are also sensitive to the differences in the intens- 

 ity of light, remaining in those places where the 

 light is weakest. It seems, too, when one or more 

 animals settle down anywhere, that the others stop 

 more readily in that place. This is an illustration of 

 " sociability " among lower animals. It is probably 

 an instance of chemotropic irritability. The surface 

 secretions emanating from the worm's body have a 

 quieting influence on other worms of the same kind ; 



