38 A Guide to the Zoological Collections 



Not only so: but a respectable number of species are 

 common to the two areas, and that not only in the case 

 of wandering species that may live in the surface drift, 

 or of widely-ranging deep-sea species, but also in the 

 case of shore-keeping forms. For instance, Lobotes 

 surinamensis, a Sea-perch that lives in brackish water 

 and estuaries, is found on the Atlantic coasts of Tropical 

 America and on the shores of the Indian Ocean from 

 Africa to China, and has once been taken in the Medi- 

 terranean, off the Sicilian coast. Hoplostethus mediter- 

 raneum has a somewhat similar distribution, and there 

 are at least a dozen other species which, though not 

 found in the Mediterranean, are common to the Atlantic 

 approaches of that Sea and the Indo-Pacific. 



The conclusion therefore seems irresistible that a 

 large part of the present fish-fauna of the Indian Seas 

 is derived from a great tropical Mediterranean Sea, of 

 a former geological period, that stretched from the Gulf 

 of Mexico, eastwards, halfway round the globe. 



THE FAUNA OF THE DEEP SEA. 



More than 150 species of fishes are known to live in 

 the depths of the Indian seas, down to 1500 fathoms. 

 Some of them undoubtedly live at the bottom, but the 

 great majority probably swim about in the middle 

 depths. 



The conditions under which many of them must live 

 are most peculiar. In the first place, the direct heat 

 and light of the sun are cut off — as in a much minor 

 degree they are cut off to our own daily observation by 

 clouds and fogs — by the overlying volume of water, so 

 that the bottom of the sea, at great depths, is cold and 

 quite dark : at a depth of 200 fathoms it is supposed to be 

 quite dark, and the temperature in these seas, is about 



