upon the Distribution of the Fauna of the JEgean Sea. 171 



of temperature in those descending regions, corresponding to 

 the temperature of the parallel of latitude in which the species 

 are identical or analogous. 



I have before pointed out that between the littoral and fourth 

 or fifth region there is a difference of temperature amounting 

 to 25°, and sometimes even to 30°; the upper division of the 

 littoral zone ranging from 76° to 84° during seven or eight 

 months in the year ; whilst in the lowest regions, there appears 

 to be a permanent temperature as low as 55~°. Thus we have 

 a region of depth of a temperature corresponding to the sum- 

 mer temperature of a high northern latitude. It seems natural, 

 therefore, that in the fauna of one locality should be found 

 identical or analogous species with the other, considering how 

 great is the influence of temperature in governing the distri- 

 bution of terrestrial fauna and flora. And I am of opinion, 

 that increased density from depth is not so great an antagonist 

 to the existence of animal life as is generally supposed. Air- 

 breathing animals can soar to highly rarified regions without 

 inconvenience of respiration. The inhabitants of 100 feet 

 above the sea feel the same freedom of circulation that the 

 inhabitants of 10,000 feet feel. It is temperature, and local 

 conditions partially arising from it, that limits the ascent and 

 existence of life. So does the same law appear applicable to 

 marine animals which breathe the medium they inhabit. 

 When we examine the members of the lower regions of depth, 

 we find them as fragile and delicate, if not more so, than their 

 brethren above. I may mention that the Ophiurida range 

 into all regions yet explored, one species being a traveller 

 from the highest to the lowest. At the depth of 320 fathoms 

 at about forty miles east of Malta, I recently procured a small 

 Sipunculus, which appeared however to be peculiarly adapted 

 to the conditions of that depth ; its density, it is said, tending 

 to hold light bodies in suspension : the posterior extremity of 

 the Sipunculus was truncated so as to form a circular disc, by 

 which it secured itself to the bottom, or any solid body found 

 there : whilst in my possession, it thus attached itself to the 

 bottom of the glass of sea-water in which it was placed. 



I shall now proceed briefly to investigate the fauna of each 

 region of depth, as marked out by Professor Forbes. 



The first or littoral zone he limits to two fathoms, or twelve 

 feet below the surface : but this, although of so small an amount, 

 the Professor shows "has two well-marked subdivisions; viz. 

 first, the upper or tidal zone of about two feet, between air 

 and water, the inhabitants of which are remarkable, as being 

 such as have a wide geographic range : eight out of the 

 eleven species peculiar to it are widely distributed in the 



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