ON THE ROLE OF AN INTEGUMENTARY PIGMENT IN 

 PHOTORECEPTION IN HOLOTHURIA. 



By W. J. CROZIER. 



{Contributions from the Bermuda Biological Station for Research, No. 117, and 

 from the Hull Zoological Laboratory, University of Chicago, Chicago.) 



(Received for publication, May 29, 1920.) 



The experiment recorded in this note was undertaken in 1917, 

 with a view to testing the notion (Crozier, 1914-15) that the fluores- 

 cent, greenish yellow, integumentary pigment characteristic of some 

 members of the genus Holothuria is concerned with their photic 

 sensitivity. A functional connection of this sort was suspected be- 

 cause the presence and relative amount of the pigment seemed to be 

 correlated with the degrees of photic stimulation in three species of 

 Holothuria studied at Bermuda; a pigment of similar nature seems to 

 occur (Crozier, 1917) in the West Indian Actinopyga agassizii which, 

 like these species of Holothuria, is negatively hehotropic. Dubois 

 (1914), in his book, had earlier suggested a photosensitizing role for 

 the fluorescent (dichromatic) substances occurring in various worms 

 and echinoderms. It was expected that the stimulating power of 

 sunlight transmitted by a screen of this pigment might be different 

 from that of sunlight directly falling upon one of these holothurians. 

 It is known that in photochemical action the effects of light are due 

 to the absorbed wave-lengths. With the skin pigment of Holothuria 

 'there is pronounced absorption in the visible spectrum. Hence it was 

 assumed that light deprived of these absorbable rays, by preliminary 

 passage through a layer of the pigment, might perhaps be less effective 

 for excitation. This expectation was not realized. 



The species employed was Holothuria captiva, a form very sensitive 

 to light, which was usually found under stones; in dark caves, how- 

 ever, it was found creeping freely over the walls, showing that its 

 occurrence under stones along the shore is in all probability due to its 

 photic irritability. 



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