FISHES/ 263 



scales, and composed of a very dense cartilage, which, 

 in some parts, is nearly two inches in depth. 



The pectoral fins are short and broad, and their 

 position denotes that they have a vertical action. 

 The dorsal and anal fins are long, pyramidal, and placed 

 opposite to each other; while the tail-fin joins the two 

 last, and constitutes a large segment of the circle formed 

 by the entire body of the fish. A peculiar soft structure, 

 or hinge, intervenes between the fins and the dense 

 texture of the skin, and serves to facilitate their motions. 

 The gill-aperture has a semilunar form, and is placed 

 immediately in front of the pectoral fin. 



The skeleton of this fish is chiefly composed of a 

 white cartilage, but the jaws are furnished with two 

 strong bony plates or teeth, each of which is continuous, 

 and consequently denotes that the fish is of the genus 

 Diodon ; although some authors have placed it amongst 

 the Tetrodons, which have their jaw-plates, or teeth, 

 divided by a fissure in their centre. The contents of the 

 stomach, in the examples we examined, were small red 

 cuttle-fish. 



The eye of the Sun Fish is large, and possesses the 

 following remarkable peculiarity: the conjunctiva, or 

 outer membranous coat, of this organ is white, thick, 

 but loosely attached to the parts beneath, and lies in 

 small circular folds ; while behind it, and around the 

 eye-ball, there is a sack of gelatinous fluid, occupying 

 the back part of a capacious orbit. When the fish is 

 alarmed for the safety of its eye, as by the approach or 

 contact of a foreign body, it displays a power of re- 

 tracting the eye-ball within the orbit; when the ge- 

 latinous fluid behind it is displaced, starts forward, 

 distends the loose folds of conjunctiva, and covers and 

 protects the eye more effectually than the eye-lids of 



