28 CLASSIFICATION AND ADAPTATION 



not find that northern or Arctic species of fish in 

 general have the scales more developed than southern 

 species. 



The Dab, which occurs in the same waters as the 

 Plaice, has the spines more spinulated than any of the 

 forms of plaice above mentioned, therefore the 

 absence or slight development of spinules in the 

 typical Plaice is not explained by physical conditions 

 alone. Freshness of water again will not explain 

 the difference of the structure and distribution of 

 scales in Flounder and Plaice, considering the variety 

 of squamation in fishes confined to fresh water. 

 Still less can we attribute any of the peculiarities of 

 scales to utility. We can discover no possible 

 benefit of the condition in one species which would 

 be absent in the case of other species. We can go 

 much further than this, and maintain that there is 

 no reason to believe that scales in general in Teleo- 

 steans, or any of their various modifications, are of 

 special utility : they are not adaptive structures at 

 all, although of great importance as diagnostic 

 characters. It may be urged that in some cases, 

 such as the little Agonus cataphractus or the Sea- 

 horse among the Syngnathidae, the body is pro- 

 tected by a complete suit of bony armour; but 

 accompanying these in the littoral region are numer- 

 ous other species such as the Gobies, and even other 

 species of Syngnathidae which have soft unpro- 

 tected skins. 



Similarly with colour characters : the power of 

 changing the colour so as to harmonise with the 

 ground is obviously beneficial and adaptive, but in 

 each species there is a specific pattern or marking 

 which remains constant throughout life and has 



