PRESIDENTIAL ADDRESS. 19 



imitate in almost all superficial characters of the shell the 

 biologically wholly different pondsnails and landsnails. 



Similar exigencies of the environment have provoked similar 

 mechanical responses in the shelly parts, a result wholly in 

 harmony with the modern postulates in biological science. 



As might be expected ot descendents with modification there 

 are greater similarities between the larval shells of benthal spe 

 cies and those of their shallow water relations, than between 

 the parts of the shell, which are of later growth in the same 

 forms. There is one notable difference however. In the deep 

 \vater forms the nucleus is frequently larger than in their shal 

 low water analogues. It would seem as if the conditions of 

 the depths were such, that, of a small number of large larvae, 

 more are likely to survive than of a larger number of smaller 

 ones ; or at least that that form of larval growth is more useful 

 to the species. 



These details will serve to show the multiplicity of facts to 

 be accounted for and the opportunity for advancing science by 

 a study of abyssal conditions and their effects upon the animals 

 subjected to them. Without claiming any unique importance 

 for the theories advanced in the foregoing remarks it may still 

 be said that the subject is one of the very greatest interest. 

 Perhaps experiments upon shallow water forms, artificially 

 subjected to pressure may at some future time enable us to 

 penetrate more deeply into the mysteries of life in the abysses. 



The attempt to prepare a summary of bathymetrical data for 

 the deep sea fauna of any region yet investigated, is most un 

 satisfactory in its outcome from the paucity of data. Most of 

 the species of any collection are represented by the shells alone, 

 which may have been as millions are daily disgorged by 

 fishes, and never have lived at the depth from which they were 



