2 Prof. T. Fuctis on the Deep-sea Fauna. 



The passage of the littoral into the deep-sea fauna is not 

 effected suddenly and without transitions, but gradually, the 

 different littoral animals ceasing and the different deep-sea 

 animals commencing at different depths. 



In this way a number of zones of depth may be distinguished 

 between the shore-line and the greatest depths, each of them 

 characterized by a definite assemblage of animals ; and hence 

 at the first glance it appears to be very much a matter of 

 arbitrary choice where we draw the boundary between littoral 

 and deep-sea faunas. 



But when we go thoroughly into the matter, and in so 

 doing take into account not so much the distribution of indi- 

 vidual species or classes, as the distribution of the animals in 

 its great fundamental features, we arrive at the conviction 

 that this apparent indefiniteness really by no means exists, 

 but that there is rather a perfectly definite region in which a 

 change in the fundamental features of the fauna is effected, so 

 profound and general, that in comparison with it all other 

 subdivisions appear to be only divisions of subordinate rank. 



The facts upon which this view is based are as follow r s : 



It is well known that marine plants, and indeed botli sea- 

 weeds and the Phanerogamia of the sea, as organisms de- 

 pendent upon light, only extend down to a moderate depth 

 in the sea; indeed we may in general fix this limit at the 

 depth of 30 fathoms*. These submarine forests and meadows 

 of marine plants, however, are the seat of an exceedingly rich 

 fauna ; and a great part of this has its existence dependent 



upon these plants, and is therefore bound to them in its occur- 



rence. 



A second prominent shallow-water assemblage of animals 

 is presented to us in the coral-reefs. The reef-building corals 

 attain the maximum of their development in a zone from 1 to 

 8 fathoms. Lower down they decrease perceptibly ; and a 

 depth of 20 fathoms is generally regarded as their extreme 

 limit. The coral-beds, however, are also the gathering-grounds 

 of an extremely rich fauna ; and the animals composing this 

 are at the same time often so remarkable and peculiar, and so 

 closely connected in their occurrence with the coral-banks, 

 that we may characterize them at once as reef- or coral-animals 

 as, indeed, one sometimes speaks in this sense of coral-fishes, 

 coral-mollusks, &c. The unparalleled wealth of marine 

 animals which is displayed by the tropical part of the Indian 



* Only Nullipore8 extend into greater depths, and are found, for ex- 

 ample, in the Mediterranean, according to Carpenter, down to 150 

 fathoms. 



