FISHES AND SEA-SQUIRTS. 297 



to their surroundings as bird in air or mammal on land. 

 Into the details of structure we cannot go, but almost any 

 shore fish will serve to give you a general idea of the general 

 characters of a fish. 



In the first place, with the exception of skate or dog-fish, 

 occasionally thrown up after storms, all our common fish 

 belong to the bony fish, or Teleosteans, which are geologically 

 recent animals, and display the fish-like characters in their 

 highest degree of development. But as the fish in its 

 highest development is, above all things, an animal adapted 

 for life in mid-ocean, for swift movement, we must expect 

 the forms available on the rocks to display the piscine 

 characters in a less typical form than their brethren of the 

 open sea. The fish which are always to be found in the 

 rock pools are those which are specially adapted for that 

 life, and which would be as helpless in the open sea as the 

 strong swimmers of that open sea would be if confined in 

 such pools by any untoward circumstance. Such shore fish, 

 therefore, display various peculiarities of form which 

 distinguish them from the more typical fish of the open sea, 

 but these peculiarities are usually of the kind known as 

 adaptive that is to say, they occur in different fish not as 

 the result of inheritance from a common ancestor, but as an 

 adaptation to a common environment. Thus shore fishes 

 are often without scales, they often have an eel-like body 

 adapted for creeping through rock crevices, they may be 

 flattened to enable them to pass their lives on the bottom, 

 and so on. 



Before proceeding to describe the peculiarities in detail, 

 let us look at a typical fish, choosing a member of the great 

 cod family, which includes many important food fishes. If 

 you idly row about in a boat in the summer time not far 

 from shore, or watch the streams of sea-water which ebb 

 and flow through the deep channels of the rocks, or gaze 

 down into the water from a pier or landing-stage, you are 

 certain at some time to see shoals of fish of a beautiful 

 greenish tint, which dart and wheel and turn in the water 

 like swallows in the air, showing gleams of glistening silver 

 at every movement. So abundant and so fearless are they 

 that even the simple artifice of a bent pin and a piece of 

 mussel will often produce several specimens, when employed 



