SENSORY REACTIONS OF CHROMODORIS ZEBRA 263 



foot being applied to the substratum. The whole body can, 

 however, be supported by the use of a small part only of the 

 foot; thus C. zebra has sometimes been observed to creep over 

 the edge of a submerged rock, the body of the animal projecting 

 horizontally beyond the edge, or its anterior part being even 

 sharply elevated, until only a centimeter or so of the posterior 

 region of the foot served as a hold-fast. Chromodoris can also 

 swim attached to the surface film of quiet water, but has not 

 been observed to do so in nature. (This behavior has been ob- 

 served in another nudibranch, FaceUna goslingi, at the time of 

 its reproductive activity.) 



Fig. 1 Outline figure of Chromodoris zebra; dorsolateral view from the right 

 side (after Crozier, '18 d). 



Especially in the mangrove creeks already spoken of, C. zebra 

 is found in localities where eel-grass grows in great profusion. 

 It creeps up the blades of eel-grass and is often found at the very 

 tip. In connection with this habit it is important that the foot, 

 although perfectly flat and without a trace of median division, 

 when in contact with a flat surface, exhibits a most pronounced 

 tendency to fold together, so that the lateral halves of the whole 

 surface of the foot are in contact. This occurs whenever the 

 whole or a part of the foot is removed from a substratum, and 

 makes it possible for the nudibranch to climb the flat-bladed 

 eel-grass. In C. roseapicta no such behavior of the foot is seen, 

 and this species lives under stones along the shore, never coming 

 into contact with eel-grass. 



