SENSORY REACTIONS OF CHROMODORIS ZEBRA 307 



takes place (Crozier, '18 d) ; still, it is possible, for one of the indi- 

 viduals is commonly more active than the other in the maneuvers 

 preliminary to copulation. 



VI. SUMMARY 



1. Physiological evidence is adduced for the existence in Chro- 

 modoris zebra of differentiated receptive mechanisms mediating 

 reactions to tactile, chemical, and shading stimulation, to the 

 constant intensity of Hght, and perhaps to heat. 



2. Locally, responses of the general integument and all of the 

 outgrowths of the body, gill plumes, 'rhinophores,' tentacles, 

 pharynx, depend upon locally contained, peripheral, non-synaptic 

 networks. In the gill plumes, and probably in the other pro- 

 jecting parts, these nerve nets are polarized. 



3. Reactions involving parts distant from the site of activation 

 depend upon central, ganglionic, transmission. The peculi- 

 arities of heterolateral response; of irreciprocal conduction be- 

 tw^een the several homolateral parts; and of behavior following 

 strychnine injection, show this central nervous system to be 

 essentially synaptic. 



4. The nudibranch is positively phototropic, the chief recep- 

 tive organs probably being the eyes. The branchial collar is 

 also sensitive to light, which causes the gill plumes to be ex- 

 panded. The gill plumes react by contraction when they are 

 shaded; this response is very variable. When sexually ripe, 

 Chromodoris is negatively geotropic. It is negatively rheotropic 

 to strong water currents, the directive organs being the 'rhino- 

 phores.' Vibrations transmitted through the water are not 

 responded to. Temperatures of 31° to 32°C. induce negative 

 reactions, Chemotropic reactions to body secretions of other 

 individuals lead to conjugation; 'olfactory' stimulation (which 

 does not essentially involve the 'rhinophores') as well as 'gusta- 

 tory' stimulation (of the lips) are concerned in this behavior. 



5. The locomotion of Chromodoris is primarily muscular, not 

 ciliary, the active part being the outer lateral margins of the 

 foot, which suck locally. Progression is strongly polarized in 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 29, NO. 2 



