SENSOEY REACTIONS OF CHROMODORIS ZEBRA 



279 



volume and velocity. The habitat of this animal is preemi- 

 nently within the semienclosed lagoons or sounds at Bermuda, 

 where tidal currents must frequently be encountered; it does not 

 occur upon the reefs. It was important to discover the nature of 

 the animal's rheotropism, if it should be found to be oriented 

 by water currents. Since the usefulness of information upon this 

 point lay in its application to the natural movements of the ani- 

 mal, the experimental work was done in the field. Laboratory 

 tests, moreover, w^ere found unsatisfactory because water cur- 

 rents of sufficient volume could not be employed conveniently. 



Fig. 3 Chart of a portion of Fairyland Creek (F. C), showing the situation 

 (cross within a circle) for testing the behavior of C. zebra in tidal currents (see 

 text). A is drawn to a scale of 6" to 1 mi. B is an enlarged sketch of the region 

 within the rectangular area surrounded by dashes in A. 



An appropriate situation was found at the western end, or 

 mouth, of Fairyland Creek (fig. 3), in a locality where hundreds of 

 the animals w^ere living at the time the experiments were made, 

 and involving, therefore, water currents normally encountered 

 by the nudibranch. 



At the period of the falling tide the currents in the location 

 selected were as shown in figure 3. The observations were at 

 first confined to sunny days. When low water or high water 

 occurred at about midday — no water then (for a short period) 

 flowed across the channel indicated — the sun was sufficiently 



