LIGHT PRODUCTION IN CEPHALOPODS. l6l 



one of the most splendid of Nature's products. Its existence was, 

 however, of short duration, though I had placed it in a large 

 vessel of water. Probably it lives at great depths." 



Although not mentioned by Hoyle, the next student whose 

 published observations concern us was none other than Charles 

 Darwin. Among the melange of odd notes in the course of his 

 account of the voyage of the "Beagle" ('60, pp. 7-8) appears 

 the following: "I was much interested, on several occasions, by 

 watching the habits of an Octopus, or cuttle-fish. . . . I observed 

 that one which I kept in the cabin was slightly phosphorescent 

 in the dark." As we have already seen, photogenic organs or 

 tissues are practically unknown among octopods, so that this 

 observation would be quite an anomalous and puzzling one, 

 were it not for the at least plausible explanation that the phe- 

 nomenon in this instance as so many others in the literature of 

 biophotogenesis was due not to the active functioning of any 

 tissues of the cephalopod itself, but to bacterial infection or even 

 to the presence of effulgent Protozoa in the slime surrounding 

 its skin. Another possibility which occurs to me is that the 

 animal may not have been examined in absolute darkness, but 

 that sufficient light penetrated into the chamber, though imper- 

 ceptible to the unadjusted human eye, to enable the iridocytes 

 in the skin of the octopus to yield a pseudo-luminous reflection, 

 analogous to that so notorious in the case of the eyes of many 

 mammals. The description by Giglioli of luminescent specimens 

 of a squid which he identified as " Loligo sagittaliis" and certain 

 Chilean octopods, referred to by Holder in the quotation given in 

 the next paragraph, may be susceptible of similar explanation. 

 To the original of this work with the description of his observa- 

 tions I have unfortunately not been able to gain access. For 

 my own part I have on several occasions attempted to discover 

 similar properties in captive specimens of the common southern 

 California devilfish, Polypus bimaculatus (Verrill), but so far 

 with only negative results. Final settlement of the question 

 can only be accomplished by careful experiment. 1 



1 Since this paragraph was put in type I am reminded that Tryon ('79, p. 131) 

 in his paraphrase of the description of Tremoctopus gracilis (Souleyet 1852) says 

 that this species is " phosphorescent and with metallic reflections when living." 

 I have been unable to check this observation by reference to the original work of 

 Souleyet. 



