MELANOPHORE A TYPE OF SMOOTH MUSCLE CELL 199 



II. Effect of Light 



Through the investigations of Arnold ('41), Brown-Sequard 

 ('47), Steinach ('92), Magnus ('99), and Franz (loc. cit.) we know 

 that the excised iris of certain elasmobranchs (Acanthias), tele- 

 osts (Anguilla) and amphibians (Rana) responds to ihumination 

 by a contraction of the sphincter pupillae. 



Hertel ('07), first succeeded in demonstrating a direct response 

 to stimulation by light in the chromatophores of the cephalopods 

 Sepiola, Octopus and especially Loligo. In this case the reac- 

 tions of the chromatophores are due to contractions and relaxa- 

 tions of the radially arranged smooth muscles. The active phase 

 is here the expanded one, elicited by the contracting radial mus- 

 cles i.e., it is the reciprocal of the condition in the melanophores 

 of lower vertebrates. Hertel found that ultra-violet light of 

 280 fxfi produced an almost instantaneous local expansion of all 

 chromatophores. Blue rays of 440 mm and yellow rays of 558 mm 

 of equal intensity also gave a distinct, but somewhat slower 

 expansion. 



I have shown (loc. cit.) that the expanded melanophores of 

 Fundulus respond to ultra-violet light (280 mm) by a rapid and 

 reversible contraction. I was unable however, in a series of 

 trials with different regions and intensities of the visible spectrum 

 to obtain contractions of Fundulus melanophores. Following 

 practically the same technique as in my experiments with Fun- 

 dulus, Laurens ('15) has recently reported contractions by ultra- 

 violet light in expanded melanophores in pieces of the skin of 

 Amblystoma larvae. Hertel (loc. cit.) had previously found that 

 the melanophores of Triton larvae responded to ultra-violet, 

 blue and yellow rays by contracting. He used the same wave 

 lengths and intensities as in his experiments with cephalopods 

 (vide supra). In this case, as in so many of the older experi- 

 ments, the presence of a complete nerve mechanism and blood 

 supply presents the possibility of secondary complications. In 

 the case of Fundulus and Amblystoma, however, I believe the 

 results to be free from this objection. 



