274 W. J. CROZIER AND LESLIE B. AREY 



agent be on the caudal extremity of the foot or on the dorsal 

 surface of the caudal veil itself (Crozier, '17 a). If strongly 

 stimulated at one point on its dorsal surface, the projecting 

 mantle margin is turned sharply dorsalward. Stimulation of the 

 caudal veil leads to pronounced local contraction of the body 

 musculature at that level, accompanied by contraction of the 

 projecting 'tail' of the foot (analogous to the 'head response' at 

 the anterior end of the animal). The pecuharities in the be- 

 havior of the caudal veil are related to the functioning of the 

 large mantle glands, of which mention has already been made. 



The peripheral edge of the foot is not very reactive to touch, 

 excepting at its truncated anterior end. There, especially at 

 the faintly projecting corners, corresponding to the place of origin 

 of the ' foot tentacles' in other nudibranchs, it is very sensitive, a 

 single touch causing head and tentacles to retract. Here again 

 the response tends strongly to be homolateral. Stimulation of the 

 lateral edge of the foot causes the foot to fold together lengthwise. 

 This is also true of the sole of the foot (e.g., of an individual 

 swimming at the surface film) ; a very distinct line, about 1 mm. 

 broad, which owes its appearance to the vertical, dorsalward 

 contraction of the foot muscles, makes itself apparent even when 

 the foot may not fold together. Touching the margin of the 

 'tail' of the foot induces deep local puckering, and that part of 

 the foot itself is pulled forward and upward. 



The pharynx, when extended, is found very sensitive to 

 touch. The lips of the fully protruded proboscis are relatively 

 insensitive, but the very faintest touch upon its lateral wall 

 leads to violent retraction of the whole head region ; the pharynx 

 is itself also momentarily introverted. Here, again, the reac- 

 tion tends to be homolateral, as in all the responses of the head 

 region. The oral area in animals with retracted proboscis is 

 not so sensitive to touch as are the tentacles. In normal creep- 

 ing it usually happens (fig. 2) that the proboscis is partially 

 everted, so that a portion of its surface, exceedingly sensitive to 

 touch, is brought into immediate relations with the surface over 

 which the animal crawls. One-sided stimulation of the pharjnix 

 causes the homolateral 'rhinophore' to retract; stimulation of a 



