INTEGUMENTARY PHOTOSENSITIVITY IN A MARINE FISH 261 



thirdly, to ascertain, if possible, any variation in the degree of sensi- 

 tivity manifested by various regions of the integument. The probable 

 location of the photo-receptive end organs, whether they lie in the integu- 

 ment or, as Payne ('07) has suggested, within the spinal cord, was also 

 considered. During the course of the work several incidental prob- 

 lems arose, principally the questions of the physico-chemical nature of 

 the effect of light upon the sense organs and the phenomenon of their 

 exhaustion. Some suggestive data were obtained on these points but 

 it is not the purpose of this paper to attempt their description and ex- 

 planation in detail. 



C. Material and methods 



The hamlet, or grouper, proved to be a very favorable animal for 

 these experiments because it is unusually hardy and recovers quickly 

 and completely from severe operations, apparently manifesting no ab- 

 normalities of behavior. 1 In order to determine the characteristic reac- 

 tions of the fish, normal individuals were studied first; but all subse- 

 quent investigations were conducted with hamlets whose eyes had been 

 enucleated at least twenty-four hours previous to the time of the ex- 

 periment. All fishes were kept in a large spawning pool which was 

 supplied with a stream of fresh sea-water. It was usually necessary to 

 prepare fresh individuals every second or third day, because fishes kept 

 for a longer time manifested variations in response which were probably 

 caused by hunger, fatigue and the loss of eyes. 2 In order that exhaustion 

 of the photoreceptors might not modify the responses, each fish was 

 used for only one, or at most two, sets of experiments embracing from 

 six to twelve tests each. 



The specimen under investigation all experiments were conducted 

 at night was placed in an aquarium whose sides were of glass and 

 whose top, bottom and ends were of an opaque material. After the 

 fish had become habituated to the new environment its integument was 

 illuminated with light from electric lamps of various moderate inten- 



1 This characteristic can hardly be exaggerated. The fishes endure the sever- 

 est of operations, either on the central nervous system or on the body, with re- 

 markable resistance. 



2 The loss of eyes seems to cause an increase in the activity of some cutaneous 

 faculties, i.e., sensitivity to tactile and rheotropic stimuli; but the phototropic 

 responses, on the other hand, are consistently retarded. It is likewise almost 

 impossible to induce blinded fishes to eat and their olfactory responses are more or 

 less retarded. These facts are interesting as showing something of the role of 

 optic stimuli in the life of the normal fish. 



