DEEP SEA LIFE IN THE BAY OF BENGAL. 547 
inorganic environment ; (2) the necessity to kill and eat ; (3) the necessity to 
avoid being killed’and eaten, and (4) the necessity to obtain a mate. 
Before proceeding to consider the play of these four factors in the depths 
of the sea, we must briefly explore these depths and discover the nature of the 
first factor. Comparing the subaqueous surface of the sea bottom with the 
subaérial surface of the dry land, we find a great contrast between the two, 
The surface of the dry land is sculptured and diversified in multitudinous 
ways by all those forces classed by geologists as ‘epigene—i.e., by rain, by 
runnels and streams and rivers, by alternating periods of moisture and drought, 
and of heat and cold, by ice, by winds, by movements of the sea itself, even 
by plants. On the floor of the ocean none of those epigene forces are present, 
and in consequence there is very little diversity of surface. We find, it is true, 
great plains and great valleys and great mountain-chains—the Bay of Bengal 
for instance is a vast plain nearly 1,000 miles in greatest breadth, broken only « 
by the one long narrow mountain-chain, which at places rises above the surface 
of the sea as the Andaman Islands—but everything is on a vast and monotonous 
scale, without diversity because there are no sculpturing forces at work, 
no inequalities of temperature, no alternating periods of heat and cold, no 
winds, no movements of the water (for waves are quite superficial, and even 
great currents, such as the Gulf Stream, do not extend to any great depth below 
the surface), no plants. 
Another great difference between the surface of the land and the bottom 
of the depths of the ocean is that the bottom of the ocean is entirely screened 
from the heat and light of the sun by the intervening mass of water. Every 
one here is familiar with the fact that the intervention of clouds, which are 
simply finely divided masses of water, between the sun and the earth’s surface 
results in gloom and in a reduction of temperature, Now apply this familiar 
phenomenon with thousandfold intensity to the bottom of the ocean, between 
which and the sun there is interposed, not for a day or two a layer of cloud, 
but for ever a volume of water often several miles thick. Even in 15 fathoms 
depth, as seen by the water-glass on a fine sunshiny day, the light that reaches 
the bottom is much subdued, giving more the appearance of moonlight than 
of direct sunlight. Experiments by Messrs. Fol and Sarasin in the clear waters 
of the Lake of Geneva, in winter time, proved that sunlight there does not 
penetrate to a greater depth than 155 fathoms. They sunk photographic 
plates, suspended from a buoy, to various depths by night, and left them 
exposed all the following day, with the result that at about 155 fathoms the 
plates were unaffected. In the open ocean, where there is absolutely no sedi- 
ment, and in the tropics, where the sun’s light is fiercest, it is generally allowed 
that no light whatever penetrates to a greater depth than 200 fathoms, Below 
that depth all is eternally dark. 
Not only is the sun’s light cut off. Weknow how clouds shield us from 
the sun’s heat rays, and similarly at the bottom of the ocean the sun’s heat is 
