MOVEMENTS IN THE VISUAL CELLS 179 



F. INTERRELATION OF INTEGUMENTARY PHOTO-RECEPTORS ANT) 

 RETINAL ELEMENTS 



The skin of several lower vertebrates has been sho^^^l to be 

 sensitive to hght. Among the fishes, Eigenmann ('00) stated 

 that certain bhnd forms hving in caves gave motor responses 

 when stimulated by light, the photo-receptors presumably being 

 located in the skin. Parker ('05) followed up some negative 

 results obtained by one of his students on Fundulus by an investi- 

 gation on ammocoetes, and proved that the integumentary 

 nerves were sensitive to light, causing movements of the animal 

 that were both 'phototropic and photodynamic' A photo- 

 receptivity of the skin of certain other vertebrates was first 

 demonstrated by the following workers: Graber ('84) on Triton: 

 Dubois ('90) on Proteus; Kordnyi ('92) on the frog; Carleton 

 ('03) on Anolis; and Eycleshymer ('08) on Necturus. 



Englemann ('85) co\'ercd the heads of dark-adapted frogs 

 with a velvet cap and exposed the bodies to sunlight. Under 

 these conditions, he asserted that in 15 minutes the pigment 

 and cone cells assumed the maximal light position, whereas 

 the same elements in control experiments conducted in the dark 

 remained unchanged. Illumination of the skin for longer periods 

 was said to result in a falling off ('herabsteigen') in the exjxmsion 

 of the retinal pigment and to a weakened response on the part 

 of the cones. From these results he concluded (p. 507) : ". . dass 

 Zapfen und Pigment des Auges von entfeniten Korpergegenden 

 aus reflectorisch in Bewegung gebracht werden konnen." 



Fick ('90), in repeating this experiment of Englemann. 

 found the pigment in an expanded condition while the frogs, 

 ready for the test, were still in the dark, and after supplementary 

 experimentation of various kinds he decided that pigment ex- 

 pansion accompanied disturbed respiration. In the case under 

 consideration the velvet hood was supposed to have caused partial 

 asphyxiation. 



Koranyi ('92) refers to the similarity in the responses of the 

 retinal pigment resulting either from the illumination of the 

 retina or of the skin only, yet he does not state that he actually 

 observed this condition himself. 



