S. S. MAXWELL 15 



Certain peculiarities remain to be mentioned. While the responses 

 could be obtained from contact stimuli on all parts of the upper 

 surface of the head, some parts were noticeably more sensitive than 

 others. Also some parts were less likely than others to produce the 

 bilateral response. Thus the strength of stimulus used in securing 

 the tracing reproduced, rarely gave rise to a retraction of both eyes 

 when appHed a.t 5 or 6, very near the inner margin of the eye. Stim- 

 uli applied to the lower surface of the snout, even near the lateral 

 margin where the upper surface was very sensitive, were very slightly 

 or not at all effective. 



The movements which I have just described are retraction of the 

 bulbs and partial closure of the rudimentary lids, and are not at all 

 to be confused with the conjugate movements which result from 

 excitation of the labyrinth. 



The contact stimuli which elicit the eye movements in Rhinobatus 

 bring about at the same time a remarkable group of coordinated 

 movements of the fins and tail. An asymmetrically applied stimu- 

 lus, e. g., at i or 2 (Fig. 1), on the left side of the head, causes elevation 

 of the posterolateral margin of the right pectoral, P, and of the left 

 pelvic fin, V, while both dorsal fins, Dj and D^, are flexed to the right. 

 A slightly stronger stimulus causes, in addition, a bending of the tail 

 to the right and a slight elevation of the anterolateral margin of the 

 left pectoral fin. If the stimulus is applied to the right side all the 

 relations are, of course, reversed; the left pectoral ahd right pelvic 

 fins are elevated and the dorsal fins and tail are turned to the left. 

 If the animal was moving forward in the water the effect of the new 

 positions of the fins would be to alter the direction so as to terminate 

 the contact with the stimulating object. If for example the point 

 touched was at 2, Fig. 1 , on the left upper surface of the head, the left 

 side of the head and body would be lowered and at the same time 

 the animal would veer off to the right; in other words a definite, 

 negatively stereotropic, reaction would result. The fin and eye move- 

 ments are as clear and characteristic in their way as are those which 

 result from stimulation of the labyrinth. 



In the preceding paragraph I have described the effect of a moderate 

 stimulus. If a more severe stimulus is applied, whether to the 

 midline or to a point asymmetrically situated on the upper 



