288 W. J. CROZIER AND LESLIE B. AREY 



and upon the reactions shown by experiments, with the central 

 gangha eUminated, to involve central transmission tracts. The 

 progressive development of the strychnine effect, in point of time 

 after injection, upon the several responses investigated; the 

 pronounced refractory phase following each response involving 

 the strychnine effect, and the enhancing nature of the effect 

 itself, all point to the reflex nature of the nervous transmission 

 concerned, since these effects are precisely those which strychnine 

 exerts in decreasing synaptic resistance. On the other hand, the 

 local responses, as seen particularly in the gill plumes, are not 

 materially affected. Strychnine does not exert these effects upon 

 de-ganglionated Chromodoris. Consequently we may assume, 

 although we have not inquired as to the specific character of the 

 strychnine effect, that peripherally, and in the outgrowths of the 

 body wall (tentacles, pharynx, 'rhinophores,' gill plumes) there 

 are local nerve-nets concerned with local responses, that these 

 nets are characteristically polarized, and that they are domi- 

 nated by the central nervous system of the nudibranch, the latter 

 being essentially a synaptic system. 



III. PHOTIC EXCITATION 



1. Light 



Chromodoris is sensitive to light. Most of the many indi- 

 viduals tested oriented directly toward a source of sunlight or of 

 diffuse daylight. The tests were frequently made in a rectangular 

 glass dish, enclosed in a covered dark chamber admitting light 

 through a slot in the bottom of one end. Most of the indi- 

 viduals moved immediately toward the light aperture and re- 

 mained for a long time pressed against this end of the aquarium. 

 Some continued to creep around the side of the dish when they 

 came into a shadow, but ultimately, on coming again into the 

 light, oriented toward it. Orientation is direct, without trial 

 movements, and the anterior end does not react to shading; 

 neither does it respond to increase of light intensity as such. In 

 the great number of individuals which we have handled at dif- 

 ferent times, no exceptions were ever found to the occurrence of 



