INTEGUMENTARY PHOTOSENSITIVITY IN A MARINE FISH 271 



directly illuminated. It was impossible to obtain any reaction. This 

 check experiment was kindly done for me by Dr. Crozier after I left 

 Bermuda. 



It appears, then, that the posterior portion of the spinal cord of 

 Epinephelus striatus is not sensitive to electric lights of moderate 

 intensities. 



III. CONCLUSIONS 



1. At least one strictly marine fish, Epinephelus striatus, possesses 

 an integument which is negatively photosensitive. 



2. This sensitivity, expressed by negative reactions, is photodynamic 

 in character, the time of the response being inversely proportional to 

 the intensity of the illumination. 



3. The sensitivity is not the same in different regions of the integu- 

 ment; being greatest in the head, less in the tail, and least in the mid- 

 body region. 



4. The photoreceptors are completely exhausted by a sufficiently 

 prolonged exposure. The time of illumination necessary to produce 

 exhaustion is in most cases inversely proportional to the intensity of 

 the illumination a photodynamic relation.- 



5. The results indicate, also, that the effect of light may be photo- 

 chemical in nature. 



IV. DISCUSSION 



The cutaneous sensitivity of fresh water fishes to light has been used 

 by Parker ('05, p. 418) to support Balfour's theory ('81) that the ner- 

 vous elements of the eye originated from the integument and were 

 once a functional part of it. Provided that the orientation of such cells 

 is constant in the ectoderm and cord during embryonic and racial de- 

 velopment, this theory explains the perplexing inversion of the ele- 

 ments of the vertebrate retina. Parker also states ('05) his belief 

 that these light terminals (spinal nerve endings) are degenerate in 

 modern lower vertebrates and also that they may represent the tem- 

 perature terminals only of higher vertebrates, having lost the photo- 

 sensitivity which they once possessed. This view involves, if the spe- 

 cialization of function is complete, the assumption that the integument 

 of the higher vertebrates is insensitive to light unless some other 

 sense organ is regarded as the receptor and also that the lower verte- 

 brates possess some type of sensory cell which, as a receptor of radiant 

 energy, is at first more or less universal in function (Parker '03, p. 34), 



