president's address. 189 



thinner, having a difficulty in secreting lime, whilst food is scarcer 

 in the abyssal regions. He admits that the number of species 

 diminishes in proportion to the depth, thus : — 



At depths of to 1 00 fathoms 9 species were obtained. 



100 to 500 ,, 6-16 do. 



500 to lOUO ,, 2-4 • do. 



lOOU to 2900 ,, 2-12 do. 



Dr. Davidson makes a similar remark as to the Brachiopoda, that they 

 diminish in number of individuals as well as in species, in proportion 

 to the depth; for out of 125 dredgings in depths of from I to 600 

 fathoms Brachiopoda Avere brought up 22 times, while in depths 

 varying from 600 to 2900 fathoms they were obtained 16 times. 



One is struck by the fact that a shell like Area corpulenta should 

 occur oif N.E. Australia in 1400 fathoms ; south of Amboyna in 200 

 to 360 fathoms ; mid-Pacific in 2425 fathoms ; and near Juan Fer- 

 nandez in 1375 fathoms; but its relatives are found in shallow water, 

 distributed world-wide, and its ancestors date back to the Lower 

 Silurian rocks; so that it has had ample time for its cosmopolitan 

 distribution. 



The Bev. B. Boog Watson's conclusions on the examination of the 

 Scaphopoda and Gastropoda of the^ " Challenger " deserve to be 

 recorded here : — 



1. Depth, he says, is an important condition in connection with 

 Molluscan life. That is to say, there really are shallow- and deep- 

 water species and genera, though their bathymetric limits are not 

 constant. 



2. Temperature, ninch more than mere depth, seems an important 

 factor in Molluscan life. It is needless to speak here of other con- 

 ditions, such as the amount of light, food, or oxygen ; because, though 

 there are extreme differences in these respects, and though their 

 influence must be very great, still their precise amount and the nature 

 and direction of their effects are too little known to afford foundation 

 for more than guesswork. 



Pressure seemed likely to prove a very important condition among 

 those which affect animal life ;• the enormous pressure upon the square 

 inch which has to be sustained, and the fact that rapid transference 

 from even a moderate depth to the surface, is sufficient to destroy 

 life ; but these impressions were removed on recollection of the laws 

 of hydrostatic pressure and the substitution of a gradual for a rapid 

 transference from deep water to the surface. 



Temperature, however, remains as an undoubtedly important factor. 



3. Great diffei'ences in respect of depth and temperature prove 

 barriers to distribution, and so, by preventing the indiscriminate 

 commingling of species, determine and preserve distinct geographical 

 provinces. 



4. During the lapse of years accidents are likely to occur, enabling 

 species to evade obstacles which would in ordinary circumstances prove 

 insurmountable. Hence the occurrence of a living species in a fossil 



