CLASSIFICATION AND ADAPTATION 35 



for any of the other specific characters, which tend 

 in each case to form a series. Thus in size norvegicus 

 is the smallest, unimaculatus larger, and punctatus 

 largest, the last reaching a length of 8J inches. The 

 subcaudal fin-flaps are least developed in norvegicus, 

 most in punctatus ; each has four rays in norvegicus 

 and unimaculatus., six in punctatus. The shorten- 

 ing and spinulation of the scales are greatest in 

 punctatus, least in norvegicus. In punctatus there 

 are teeth on the vomer, in unimaculatus none, in 

 norvegicus they are very small. 



If we consider fishes in general, we see that there 

 is no evidence of any relation between many of the 

 most important taxonomic characters and function 

 or external conditions. In the sea Elasmobranchs 

 and Teleosteans exist in swarming numbers side by 

 side, but it is impossible to say that one type is more 

 adapted to marine life than the other. There is 

 good reason to believe that bony fishes were evolved 

 from Elasmobranchs in fresh water which was 

 shallow and foul, so that lungs were evolved for 

 breathing air, and that marine bony fishes are 

 descended from fishes with lungs ; but no reason 

 has been given for the evolution of bone in place of 

 cartilage or for the various kinds of scales. Professor 

 Houssaye, on the other hand, believes that the 

 number and position of fins is adapted to the shape 

 and velocity of movement of each kind of fish. 



If we turn to other groups of animals we find 

 everywhere similar evidence of the distinction 

 between adaptive and non-adaptive characters. 

 Birds are adapted in their whole organisation 

 for flight, the structure of the wing, of the sternum, 

 breast muscles, legs, etc., are all co-ordinated for 



