282 W. J. CROZIER AND LESLIE B. AREY 



4. Nervous relations 



1. There are several very characteristic features about the 

 sensory responses of Chromodoris; these are of considerable 

 general significance. Yet the apparent variability of these 

 responses has made it necessary to study them very carefully 

 and in many individuals. 



To local excitation, not too intense, the response is local 

 merely; to more vigorous stimulation, the response obtained 

 involves more distant structures — at the anterior end, the general 

 head contraction; at the posterior end, the caudal contraction; 



A B 



Fig. 5 Behavior of the 'rhinophores' in a water current; A showing the 

 'positive' reaction of the 'rhinophore' itself; B indicating the method of reaction 

 to local current affecting directly only the 'rhinophores.' 



likewise at the anterior end the 'reflex' involvement of other 

 structures than the one stimulated proceeds upon a conspicuously 

 homolateral plan. In the case of the tentacles and 'rhinophores,' 

 moreover, stimulation of a tentacle easily induces contraction of 

 the homolateral 'rhinophore,' whereas the reverse operation is 

 exceedingly diffcult. 



The manner in which, at the head end, additional structures 

 become concerned in reaction to the activation of distant parts, 

 corresponds precisely to the distribution of the main anterior 

 nerve trunks; and the character of the responses, particularly 

 in the apparently non-reciprocal nature of conduction between 

 tentacle or pharynx and 'rhinophore,' is strongly suggestive of 

 true reflex action. 



