SENSOEY REACTIONS OF CHROMODORIS ZEBRA 287 



that the 'rhinophore' has difficulty in being itself retracted 

 within fts pocket; this behavior is never seen normally. If the 

 anterior edge of the buccal veil is touched at one side, there 

 results, as in the normal nudibranch, a homolateral 'rhinophore' 

 retraction, and also a retraction of the gill crown, which is rarely 

 seen except under strychnine. 



After one and one-half to two hours, the pharynx invariably 

 becomes extended; if touched at the side, an exceedingly violent 

 homolateral head response is the result. If the lips be touched, 

 however lightly, both 'rhinophores,' as well as the proboscis, are 

 violently retracted. On reextension, the 'rhinophores' both 

 retract when either one is touched, but the pharynx (extended) 

 does not contract at all. Nor at any other time does 'rhinophore' 

 activation induce retraction of the pharynx. 



In all of these reactions, for example, when both 'rhinophores' 

 retract as the result of one of them being touched, it is very 

 difficult, if not impossible, to secure the double response for five 

 to ten minutes subsequent to the reaction, although each one 

 responds to local activation readily enough after a 1- or 2-minute 

 refractory period; this is true of the double response independ- 

 ently of whether the ^rhinophore' first activated or the opposite 

 one is the one subsequently stimulated. A precisely similar 

 relation appears in the other responses studied. 



This period is usually succeeded by one (two and one-half to 

 three hours after injection) during which a light tactile stimula- 

 tion of one 'rhinophore' causes both the opposite one and the 

 pharynx (still extended) as well as the tentacles and gill plumes, 

 to be retracted. 



These effects of strychnine injection become obliterated after 

 the lapse of three and one-half to four hours, under the conditions 

 used in the experiments, and the animals return to an essentially 

 normal state so far as their reactions are concerned. At no time 

 is the response of the gill crown to shading (vide infra) in any 

 way enhanced. 



4. If these results are compared with those given for normal ani- 

 mals (section -/), it will be seen that strychnine has a pronounced 

 effect upon those responses involving irreciprocal conduction, 



