SENSORY REACTIONS OF CHROMODORIS ZEBRA 273 



ceptive field for the 'rhinophore' reaction is best established with 

 the aid of mild faradic stimulation. The electrodes can be 

 placed in position without inducing local response and without 

 leading to the reaction of distant parts, owing to mechanical 

 deformation of the body wall. The receptive field of the ' rhino- 

 phore' reaction, made out in this way, agrees precisely with that 

 already given. It is much more clearly defined than in the case 

 of the gill response, as we have indicated above. Stimulation of 

 a 'rhinophore' does not ordinarily lead to a reaction from the 

 gill plumes, unless the 'rhinophore' be sharply struck or pinched. 

 The 'rhinophoral' collar reacts by constriction, sphincter-wise, 

 when touched lightly, but first of all the 'rhinophore' is re- 

 tracted. To a very light touch the stimulated part of the edge 



Fig. 2 Outline lateral view of C. zebra (anterior end) during active creep- 

 ing, showing the manner in which the lips, tentacles, anterior part of the foot, 

 and the buccal veil are related to the substratum. 



of the collar contracts locally without inducing the sphincter-hke 

 constriction and without leading to movement of the 'rhino- 

 phore.' When the 'rhinophore' is retracted as the result of 

 being itself stimulated, the collar contracts over it. 



The branchial collar behaves in a precisely similar way. 



The projecting mantle-margin, if touched dorsally or ventrally, 

 is locally depressed ventral ward. This is also true of the caudal 

 veil which carries on its ventral side the conspicuous mantle 

 glands (Crozier, '17 a). When the animal is generally disturbed 

 by being handled, or is from any other cause much contracted, 

 the margin of the mantle along the sides of the body is thrown 

 into prominence laterally, owing to the forcing of fluid into its 

 internal spaces; whereas the caudal veil continues to be bent 

 ventralward, unless the point of application of the stimulating 



