266 HOVEY JORDAN 



the stimulation by means of the tail. 7 They then usually returned to 

 the shadow, but sometimes continued toward the light until they were 

 completely illuminated. This alternation of positions is almost iden- 

 tical with that which the normal fishes executed; but in the latter I 

 did not notice any backing into the light. 



Such behavior is typical of the several individuals which were tested 

 in this manner. With few exceptions they all swam away from the 

 light ; thus being, as the normal fishes are, negatively phototropic to 

 general illumination. Their reaction time, though somewhat variable, 

 averages slightly longer than that of normal fishes, being 70 seconds 

 for the stimulus of a 60-watt lamp at a distance of about 30 centimeters. 

 A 100-watt light causes the same reaction in less time. 



2. To regional stimulation. The integuments of blinded fishes also 

 were explored with a localized light in order to determine whether the' 

 variations in regional sensitivity which the normal fishes exhibited 

 would persist after the enucleation of both eyes. The apparatus used 

 and the regions tested in these experiments were the same as those 

 which have already been described in the account of the reactions of 

 normal groupers. 



They revealed a regional sensitivity nearly the same as that of the 

 normal fishes; the head being the most sensitive, the tail intermediate 

 and the mid-body least sensitive. But the average time of reaction to 

 the same intensity of illumination was, for each region, longer than 

 that of the normal fishes. A few experiments to determine this relation 

 showed that on the average 8 the period of exposure necessary to produce 

 stimulation is increased by the removal of the eyes as follows: in the 

 head region, from 3 seconds to 8.4 seconds, or 180 per cent; in the mid- 

 body region, from 12.5 seconds to 22.5 seconds, or 80 per cent; and in 

 the tail region from 7.6 seconds to 11.5 seconds, or 51 per cent. 



This retardation, it is to be observed, varies, but not proportionally 



7 It is interesting in this connection to note that the hamlet also backs into a 

 current (Jordan '17) and swims backward into the cavities of its natural environ- 

 ment. It also uses the tail frequently as a tactile organ. The posterior part of 

 the body may, therefore, have an important sensory function. Cutaneous sen- 

 sitivity to most other stimuli (tactile, rhetropic, chemical) is very similar in its 

 distribution to that to light. A somewhat similar case is one described by Parker 

 ('05, p. 418). He states that the region of Ammocoetes which is most sensitive to 

 light is its tail, and he coordinates this fact with the burrowing habit of the fish. 



8 There were, however, as usual, a few erratic cases in which the reaction time 

 of the mid-body region was shorter than that of the tail, and others in which the 

 reaction times of the three regions were equal. 



