16 LIFE IN THE SEA [CH. 



The fishes are very unfamiliar to us though they all 

 belong to well-known groups, and it is very probable 

 that they have been evolved from shallow water 

 species. They have as a rule either very large eyes, 

 or very small ones, or they are quite blind. This is 

 what we might expect if the fishes had spread into 

 the deep from the shallow water, for evolution might 

 proceed in various directions : either an organ which 

 was inefficient under the new conditions would become 

 larger by the accumulation of small variations, or 

 being unused and useless it would disappear. In 

 most of them the tail is long and slender ; the mouth 

 and teeth are very large so that the animal has an 

 eminently predatory character, which would be a 

 consequence of the difficulty in procuring food; 

 some abyssal fish are able to devour others almost 

 as large as themselves. Their bones are fragile 

 and have less than the usual proportion of lime ; a 

 character which is common to most abyssal animals 

 which have calcareous external or internal skeletons. 

 The flesh is soft and watery. There is a general 

 absence of the pronounced colour markings of the 

 shallow forms ; they are not silvery as a rule ; and 

 there are no indications of the obliterative counter- 

 shading of the fishes usually known to us whereby 

 the upper parts are darker than the lower ones so 

 as to destroy the appearance of solidity, and render 

 the animal nearly invisible to another in the water 



