PRESIDENTIAL ADDRESS. 



Such questions are much easier to ask than to answer, in fact 

 no attempt at an answer has, so far as I am aware, ever been 

 offered to biologists. 



The looseness of tissue necessary to such a permeation is 

 conspicuous in abyssal animals, whose flabby and gelatinous 

 appearance when they reach the surface is notorious. It is 

 perhaps most noticeable in the fishes, which nevertheless are 

 often armed with formidable teeth. But under the great pres- 

 sures of the deeps it is quite conceivable that each of these 

 loose and half dissolving muscles may be compressed and re- 

 duced to a condition resembling steel wire ; and that the organ- 

 ization thus sustained may be as lithe and sinewy in its native 

 haunts as its shallow water relatives are in theirs. 



It is well known how great an influence on the distribution 

 of shallow water species is exerted by the temperature of the 

 water in which the}- live. No doubt the differences of temper- 

 ature affect the nervous system, the rate of muscular contrac- 

 tion, and the motions of the cilia by, which in mollusks many 

 of the functions of life are aided or wholly carried on. 



But it is probable that the influence of temperature is far 

 more effectively exerted upon the development of the ova, and 

 hence upon the propagation of the species, than directly upon 

 the parents. It is probable that most adult mollusks could 

 endure a very wide range of temperature if the individuals 

 were subjected to the changes by extremely slow degrees. But 

 it has been shown that a difference of one or two degrees below 

 a certain point on the thermometric scale, will destroy the em- 

 bryos of Ostrea or prevent their development so that they 

 perish. In this way the spread of the species may be effectu- 

 ally checked, though the adult shellfish may flourish without 

 difficulty in the same region. 



In the shallower parts of the Archibenthal Region, a few great 



