2 W. C. M'lntosh on the Ahyssal Theory of Light. 



1. The Abyssal Theory of Light. 



The distinguished dredgers in the expeditions were struck 

 hy the luminosity of many of the animals procured from great 

 depths in the Atlantic, such as Alcyonarian Zoophytes, Brittle- 

 stars, and Annelids. In some places, indeed, the mud itself 

 was full of luminous specks*. In their Report on the Dredg- 

 ings of 1869t, they broach the idea that the abyssal regions 

 might depend solely for their light upon the phosphorescence 

 of their inhabitants, and that this luminosity in the dark 

 abysses of the sea fulfils, in regard to the great object of the 

 supply of food, the functions performed in the upper world by 

 the light of day. In other words, the phosphorescence of an 

 animal would, on the one hand, enable it to see its prey, and, 

 on the other, would discover it to its enemies |. Moreover, 

 according to the report, since the young of certain starfishes are 

 much more luminous than the adults, it is probable that this is 

 part of the general plan which provides an enormous excess of 

 the young of many species, apparently as a supply of food, 

 their wholesale destniction being necessaiy for the due restric- 

 tion of the multiplication of the species, while the breeding- 

 individuals, on the other hand, are provided with special ap- 

 pliances for escape or defence. 



Now, without entering on the present occasion into the 

 literature of the subject (a labour which has been so ably ac- 

 complished by Ehrenberg, De Quatrefages, and other authors), 

 it will be seen, on referring to a single passage in the article 

 on this subject (Todd's Cyclopedia) by the late accomplished 

 Dr. Coldstream, that marine zoologists have long been familiar 

 with such notions. " Considering," says Dr. Coldstream, 

 '^ that in the ocean there is absolute darkness at the depth of 

 800 or 1000 feet (133-166 fathoms), at least that at such 

 depths the light of the sun ceases to be transmitted, Macculloch 

 has suggested that, in marine animals, their luminousness may 

 be ' a substitute for the light of the sun,' and may be the 

 means of enabling them to discover one another as well as 

 their prey. He remarks, ' It seems to be particularly bril- 

 liant in those inferior animals which, from their astonishing 

 powers of reproduction, and from a state of feeling apparently 

 little superior to that of vegetables, appear to have been in a 



* We shall suppose that due precautions were taken to prevent the 

 entrance of the myriads of sui-face-forms. 



t Proc. Royal Soc. No. 121 (1870), pp. 431, 432. 



X Thus a young Hyas araneus having dense tufts of Ohelia geniculata 

 waving from its carapace and limbs, must, on the one hand, like an Indian 

 beauty with her fire-flies, be the cynosure of all (predatory) eyes, and, on 

 the other, be enabled to throw such a flood of light on the food-question 

 US to distance many rivals. 



