SENSORY REACTIONS OF CHROMODORIS ZEBRA 275 



'rhinophore' does not affect the pharynx, unless it be repeated 

 several times. 



The genital papilla and the mouth of the oviduct, when everted, 

 react locally to light touch, always contracting away from the 

 point touched. They induce no general reactions of the whole 

 body. 



Chromodoris is relatively insensitive to vibrational stimuli. 

 Continued tapping of the wall of a thin glass dish containing the 

 nudibranchs may cause near-by resting individuals to begin to 

 move, owing apparently to tactile irritation of the foot. No 

 effect whatever is produced on creeping individuals, and no 

 reactions are given under any circumstances by either 'rhino- 

 phores' or gill plumes. In nature the gills, ' rhinophores, ' and 

 mantle edge are moved about by tidal currents, and the body 

 is by the same means caused to sway from side to side, with- 

 out leading to noteworthy response, save in the case of the 

 ' rhinophores' 



^, Righting: geotropism 



When the foot is removed from contact with a substrate, 

 Chromodoris contracts to one-third or one-half its normal length, 

 then subsequently becomes extended. The foot folds together 

 longitudinally. The head end, after the preliminary re-extension 

 of the body, is twisted on the long axis until the anterior part 

 of the foot can be attached. The body is quite flexible, and in 

 righting it may be twisted 180° or even 270° about its long axis. 

 The foot is attached progressively, beginning at the anterior end ; 

 nevertheless, as already described, when once attached the poste- 

 rior end is so well fixed to the substrate that the animal may be 

 fully supported by this end alone. 



The process of righting occupies about one minute, ten to 

 twenty seconds of this time being taken up with the twisting of 

 the body in the effort to secure contact by means of the anterior 

 part of the foot. The anterior edge of the foot is the only part 

 which becomes spontaneously attached in this way. Observa- 

 tions on many animals in the field, as well as in the laboratory, 

 have shown that there is no pronounced tendency for C. zebra 



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



