SENSORY REACTIONS OF CHROMODORIS ZEBRA 283 



2. On the other hand, in the case of each of the projections 

 from the body (tentacles, 'rhinophores,' particularly the branch- 

 ial plumes, and perhaps the pharynx) the local reaction of 

 each stimulated part has certain definite pecuharities, best 

 studied in the gill plumes, but seemingly identical in all the 

 parts enumerated. These peculiarities are: localized longitu- 

 dinal contraction at the immediate side of activation; circular 

 constriction and longitudinal contraction beyond (distal to) the 

 level of activation ; contraction at the base when the activation 

 is sufficiently intense, in this case involving a spreading of the 

 response to neighboring parts; a lesser reactivity when the tip 

 of the organ is activated than when it is touched near its base; 

 in the gill plumes, neuromuscular polarization such that the 

 activation spreads distally from the point of excitation; slight 

 fatiguability of the local reactions, whereas the heterolateral 

 responses (e.g., in case of the ' rhinophores' and tentacles) are 

 much more readily exhausted by repeated activation. 



The local responses are exhibited in pieces of the mantle 

 removed from the body. When the central nervous ganglia, 

 supra- and suboesophageal, have been completely extirpated, 

 stimulation of the head region near a 'rhinophoral' collar causes 

 that 'rhinophore' to be retracted, the collar closing over it, as 

 normally stimulation of a tentacle leads to its reaction, but does 

 not involve retraction of the homolateral 'rhinophore.' Tactile 

 excitation of a 'rhinophore' in a Chromodoris with the ganglia 

 excised causes the 'rhinophore' to retract, after which it is 

 slowly re-extended. 



The phenomena of local response to faradic stimulation in the 

 excised gill plumes are also substantially similar to those of the 

 individual plume in the intact nudibranch. Within fifteen 

 minutes after amputation a gill plume becomes relaxed, though, 

 like the excised tentacle of an actinian (Parker, '17), it is not 

 so fully extended as it may be when attached to the animal, 

 because no fluid is being forced into it. The relaxed, isolated gill 

 plume is fully as sensitive to touch as when forming part of the 

 normal nudibranch, the peculiarities of its reactions are identi- 



