DEEP-SEA FAUITA. 117 



long been recognised in the Atlantic and Mediterranean Tvaters of 

 Europe as occupying the one hundred fathom zone ; and it has been 

 equally observed along the coast of Brazil, the Philippines, and 

 elsewhere. The fact that almost everywhere this upper limit of 

 faunal distribution should correspond with a line of nearly uniform 

 depth is certainly very remarkable, and one that argues strongly 

 against the notion of thermal influences. For, if the determining 

 factor in vertical distribution were really the matter of temperature, 

 we should naturally expect to find the defining line between the 

 surface and deep-sea faunas to be differently located for different 

 parts of the earth's surface, rising in the polar and high temperate 

 regions, where the surface temperature of the water is itself very 

 low, and falling in the region of the tropics, whereas, as a matter 

 of fact, no such condition obtains. Indeed, on the principle gen- 

 erally entertained, there ought to be in the high northern and 

 southern latitudes no such thing as an abyssal fauna, inasmuch as 

 the thermal conditions requisite for its existence would be those 

 corresponding to the surface fauna as well, a nearly uniform tem- 

 perature extending through the sea from top to bottom. We should 

 then expect to meet with the characteristic deep-sea forms of corals, 

 brachiopods, vitreous sponges, echinoderms, &c., seemingly indica- 

 tive of a low temperature, in the littoral region, but, as is well 

 known, they do not occur there, although they are suflaciently 

 abundant in deep water. It is true that certain animals occurring 

 in the deeper parts of the warm seas are known as surface forms 

 only in the Arctic waters ; but these are inconsiderable in number, 

 and in the main uncharacteristic, so that they can scarcely be con- 

 sidered as a link uniting the littoral with the deep-sea faunas ; in a 

 general way the two are as sharply defined in the Arctic Seas as 

 anywhere else. But, if it is not the matter of temperature that is 

 principally involved in the formation of a deep-sea fauna, what is ? 

 The question does not, perhaps, at the present moment admit of a 

 definite solution ; but a suggestion thrown out in this direction by 

 Professor Fuchs deserves careful attention. After reviewing the 

 possibilities that may arise from such proximate causes as differences 

 in the chemical characters of the water, the quantity of absorbed 

 air contained in it, and currental motion, all of which must assuredly 

 be of insignificant import, this eminent authority arrives at the con- 

 clusion that the only factor which can, in any material way, affect ' 



