SPINY-FINNED FISHES, 53 



ORDER I. ACANTHOPTERYGII. 



{Spiny-finned Fishes.) 



The skeleton in this large and very natural 

 Order is composed of bone ; the first rays (count- 

 ing from the head backward), of the dorsal fin, 

 of the pectorals, and of the anal, and, generally 

 the first ray of the ventrals are unjointed, in- 

 flexible, and spinous. When there is more than 

 one dorsal, the anterior is entirely filled with 

 spinous rays. In some cases, as in the common 

 Sticklebacks, the spinous rays are unconnected 

 by a common membrane, and form free spines. 

 The ventrals are, for the most part beneath the 

 pectorals, or even in advance of them. The bod}^ 

 is clothed with scales formed of successive laminae 

 or layers of horn-like, unenamelled bone, which 

 have their free hinder margin cut into teeth. 

 The swimming-bladder is not furnished with an 

 air-duct leading into the gullet. 



Nearly two-thirds of the species belonging to 

 the whole Class of Fishes are found in this Order, 

 which are scattered over all parts of the w^orld, 

 both in fresh and salt waters. Many of them are 

 distinguished for elegance of form and beauty of 

 colour ; nearly all are fit for food, and some, as 

 the Mackerel family, including the Tunny, sup- 

 port important fisheries. 



The form of the dorsal fin is subject to much 

 variation in this Order. Nearly half of the 

 species have it divided into two, a spinous and a 



