Prof. T. Fuchs on the Deep-sea Fauna. 11 



in other words, that the littoral fauna is nothing but the fauna 

 of light j and the deep-sea fauna the fauna of darkness. 



To prove that this is actually the position of matters, several 

 other circumstances may be cited. 



Thus it must above ail be indicated that the dependence of 

 the organic world upon light not only shows itself at the 

 above fundamental critical point of 50 fathoms, but that it 

 can also be demonstrated at the subordinate degrees of intensity. 

 For example, Lorenz, in his investigations in the Gulf of 

 Quarnero, with his imperfect method of research arrived at 

 the depth of 24-30 fathoms as the lower limit of light. This 

 depth of course cannot be accepted as the actual lower limit ; 

 but it certainly forms the limit for a certain intensity ; and it 

 is not without interest that we remark that this depth exactly 

 agrees with that which is given as the limit of plant-growth 

 in the sea. 



On a former occasion I have called attention to the fact 

 that the depth already mentioned of 43-50 fathoms, found by 

 Secchi, Pourtales, and Bouguer, cannot represent the absolute 

 limit of light, but that small quantities of light no doubt pene- 

 trate considerably deeper iuto the sea, and, indeed, from the 

 analogy of Forel's investigations in the Lake of Geneva, as far 

 as 100-200 fathoms. Now. it is certainly very remarkable 

 that Carpenter states the limit to which Nullipores occur at 

 150 fathoms, and that Agassiz cites precisely the same limit 

 for the greater part of those littoral animals which extend be- 

 yond their normal boundary for some distance into the region 

 of the deep-sea fauna •. 



With their character of animals of darkness numerous 

 peculiarities in the organization and nature of the deep-sea 

 animals agree. Thus it is known that very many deep-sea 

 animals either have uncommonly large eyes, after the fashion 

 of nocturnal animals, or are completely blind ; it is also well 

 known that they are for the most part either pale and colourless 

 or unicolorous, and that varied coloration is exceedingly 

 seldom met with among them ; and, finally, it is likewise well 

 known that a very large proportion of deep-sea animals, in 

 many groups, indeed the majority, are vividly luminous. 



This last peculiarity is of special importance ; for it is clear 

 that luminosity can be of consequence only to such animals as 

 are destined to live in darkness, and, in point of fact, scarcely 

 any luminous animals are known to us from the littoral 



* From the investigations of Forel in the Lake of Geneva, of Wei^mann 

 in the Lake of Constance, &c. ? it seems to me decidedly to follow that in 

 freshwater lake.s also the bathvmetrical distribution of animals is deter- 

 mined chiefly by light 



