THE STICKLEBACKS 79 



stones, when the fish, being stunned, fall out." From this 

 not very delicate experiment Aristotle argues that fish can 

 hear. 



Twelfth Sub-Order : ACANTHOPTERYGII GASTROSTEIFORMES : STICKLE- 

 BACK-LIKE SPINY-FINNED FISHES. 



The fish of this sub-order are distinguished by the dorsal 

 fin resolving itself into isolated spines, and by the small mouth 

 at the end of a snout generally more or less lengthened. It 

 consists of but two families, the sticklebacks and the flute- 

 mouths. 



FIRST FAMILY: GASTROSTEID^E : The Sticklebacks 



Body elongated and compressed laterally. Parts of the 

 skeleton are produced and expanded to form plates covering 

 parts of the skin. There are no scales, and the place of the 

 first dorsal fin is occupied by isolated spines. The ventral fins 

 are placed on the abdomen, and contain one spine and one 

 soft ray. 



The sticklebacks consist of but a single genus, Gastrosteus, 

 wherein about ten species have been recognised ; but they are 

 such variable creatures that scarcely any two ichthyologists can 

 be got to agree as to the number of true species inhabiting 

 British fresh waters. Some authorities put it as high as six, 

 but Dr. Giinther, who certainly is not unduly scrupulous in 

 admitting to the dignity of species certain forms which other 

 naturalists refuse to regard as more than varieties, holds that we 

 have only three distinct sticklebacks the three-spined (Gas- 

 trosteus aculeatus), the four-spined (G. spinulosus), and the ten- 

 spined (G. pungitiu j). Of these the first-named is by far 

 the commonest in this country, and as I am personally un- 

 acquainted with the second, I shall do no more than mention 

 it ; taking occasion to add that it is much to be desired that 

 those who. have opportunity and inclination should devote close 



