HABITS OF MARINE ANIMALS 95 



and muscular power of an animal : the force which propels 

 their bodies or their brains is as much a matter of combustion 

 as that which is generated in a steam boiler. This respiratory 

 process is necessarily slow in all gill-breathers, which take the 

 air from the exceeding dilution in water where it does not 

 constitute one-hundredth of the mass, as compared with lung- 

 breathers where the oxygen can be supplied as rapidly as 

 needed. There is another condition of the sea which has, 

 doubtless, much retarded the. advance of its tenants : the 

 greater part of its life dwells in utter darkness. At one 

 hundred feet in depth the vertical sun yields only a twilight, 

 and below one thousand feet it is perpetual night. As a large 

 part of intellectual life depends upon the knowledge acquired 

 by sight, we easily perceive that the utter darkness of the 

 deeper sea is most unfavorable to the development of intelli- 

 gent beincrs. 



With this understanding of the general limitations of 

 marine life, we are not surprised to find that the animals 

 of the sea are almost completely lacking in habits of an 

 intellectual order. Save in a few forms, as, for instance, 

 the species of tish which weave a rude nest of sea-weed, the\- 

 make no constructions such as are so commonly produced by 

 land animals. They rarely emit any sound in the nature of a 

 sexual call ; they never dwell in organized communities of 

 a social sort ; the sexes rarely if ever mate, even for a season. 

 With them life in general has not risen above the plane of 

 mere existence. The only marine animals which have been 

 observed to have any distinct marks of intelligence are the 

 forms which have the habit of resorting to the shore, espe- 

 cially the seals, which are descended from the land animals 

 in the kinship of our bears and dogs ; and are. in fact, not 



