260 DE. C. CHILTON ON THE SUBTEREANEAN 



' Albatross ' dredgings in 1883 [105] lie points out that the colour of these deep-sea forms 

 is very striking. A few are nearly colourless, hut the majority are some shade of 

 red or orange. A few species (100 to 300 fathoms) are conspicuously marked with 

 scarlet or vermilion, but such markings were not noticed in any species from below 

 1000 fathoms. Below this, orange-red of varying intensity is apparently the most 

 common colour. He also shows that some of the species ranging down to 2000 fathoms 

 possess eyes, some of them as well developed as in corresponding shallow-water forms. 

 Summing up these facts he says : — 



" However strong may be the arguments of the physicists against the possibility of 

 light penetrating the depths from which these animals come, the colour and the structure 

 of their eyes, as compared with blind cave-dwelling species, show conclusively that the 

 darkness beneath 2000 fathoms of water is very different from that of ordinary caverns. 

 While it may be possible that this modification of the darkness of the ocean abysses is 

 due to phosphorescence of the animals themselves, it does not seem probable that it is 

 ■wholly due to this cause " [105, p. 56]. 



I wished to test this conclusion by studying the colour of animals found in the 

 deep waters of lakes, such as tliose of Switzerland, but, unfortunately, the facts that I 

 find ready to hand are not very conclusive either way. In considering the modifications 

 undergone by the deep-water species, Forel says under the head " Pigmentation " : — 

 " La couleur est generalement plus claire dans les especes littorales " [40, p. 167]. 

 He also states that Du Plessis has noticed a rosy colour in some Turbellarians from the 

 deep waters, which is not found in those of the littoral region. There does not, however, 

 appear to be a prevailing red or orange tint at all comparable to that which has been 

 noticed by Smith in deep-water marine Crustacea, or special attention would have been 

 drawn to it by Porel ; but, again, the species of Crustacea found in the deep waters of 

 the Swiss Lakes are very few in number compared with those in the deep waters of the 

 sea, and there are none of the larger forms like those examined by Smith, so that there 

 is scarcely a sufficient basis for a comparison of any value. Porel describes Niphargus 

 Forelii as " blanchatre avec des teintes rosees," and Asellus Forelii as " d'un blanc 

 grisatre, sale" [40, pp. 112, 113]. 



On the whole, however, the colour of the animals in the deep waters of the Swiss 

 Lakes appears to resemble that of the animals in caves and underground waters rather 

 than that of the inhabitants of the deep waters of the ocean ; and this would incline 

 us to imagine that the difference in colour between the two last-mentioned is due to 

 some differences of chemical composition rather than to the presence or absence of 

 light. 



Loss of Eyes. 



In all animals inhabiting caves and underground waters the eyes appear to undergo 



more or less degeneration. Schneider has described the commencement of such 



degeneration in Gammarus pulex, var. suhterraneus [96], and in Asellus aquaticus, var. 



freihergensis [97], and Moniez in Gammarus fluviatilis, var. d'Emmerin [78, p. 39]. 



Packard, who has considered the subject very fully in connection with the inhabitants 



