Ixii. PRESIDENT'S ADDRESS. 



affecting the composition of sea-bottom deposits and the supply 

 of oxygen, carbonate of lime, phosphate of lime, and other materials 

 necessary for their development, than upon conditions immediately 

 connected with depth. One of the results of the " Challenger " 

 Expedition is to know that the fauna of deep water is principally 

 confined to two belts one at and near the surface and the other at 

 and near the bottom, leaving an intermediate zone in which the 

 larger animal forms, vertebrate and invertebrate, are nearly or 

 entirely absent. Among the abyssal fauna, mollusca, Crustacea, 

 and annelida are on the whole scarce, while echinodermata and 

 porifera greatly preponderate. Depths beyond 500 fathoms are 

 inhabited everywhere by a fauna which presents generally the same 

 features throughout. Deep-sea genera have usually a cosmopolitan 

 extension. The abyssal fauna is more nearly related to the fauna 

 of the Tertiary and Secondary periods than that of the shallower 

 water. The peculiar adaptations to the conditions of their exist- 

 ence among deep-sea animals point to the struggle for existence 

 being not less severe in the deeper regions than elsewhere. 

 Phosphoric light plays an important rule in the economy of the 

 deep-sea life. Some species, in addition to large eyes, are provided 

 with a sort of bull's-eye lantern, from which streams of light are 

 thrown out at the will of the animal. Phosphorescent organs actr 

 also as a lure, or they may indicate the presence of prey or the 

 passage of an enemy. In the shallower parts of the ocean the 

 materials at the bottom are assorted and distributed by the currents 

 in a way which produces a great variety of conditions. In some 

 places there are siliceous and calcareous sands, in other places dead 

 shell?, and pebbles, rocks, and boulders prevail on submarine banks, 

 fine mud and clays in depressions. On each of these bottoms there 

 is usually a very different assemblage of animals. 



With increasing depth not only the nature of the deposits, but 

 the other physical conditions, become more and more uniform till a 

 depth is reached along the continental shores facing the great 

 oceans, immediately beneath which the conditions become nearly 

 uniform, and where the fauna likewise presents a great uniformity. 



