PISCES. 199 



always perforated by two holes, and regularly lined by a plated pi- 

 tuitary membrane. 



The cornea of their eye is very flat, and there is but little aqueous 

 humour, but the crystalline is very hard and almost globular. 



The sense of taste in Fishes can have but little energy, as a great 

 portion of the tongue is osseous, and frequently furnished with teeth 

 and other hard parts. 



The body in most of them is covered with scales, and none pos- 

 sess organs of prehension ; the fleshy cirri of some may supply the 

 imperfection of the other organs of touch. 



Teeth are found in their intermaxillary, maxillary, lower jaw, 

 vomer, bones of the palate, on the tongue, on the arches of the 

 branchiee, and even on bones behind these arches, attached like them 

 to the hyoides, called pharyngeal bones. 



The varieties of these combinations, as well as those of the form 

 of the teeth placed at each point, are innumerable. 



Besides the apparatus of the branchial arches, the hyoid bone is 

 furnished on each side with rays which support the branchial mem- 

 brane. A sort of lid composed of three bony pieces, the operculum, 

 the suboperculum, and the interoperculum, unites with this membrane 

 in closing the great opening of the gills; it is articulated with the 

 tympanal bone, and plays on one called the preoperculum. In many 

 of the Chondropterygii this apparatus is wanting. 



Fishes form two distinct series, thd^t of FisnEs properly so styled^ 

 and that of the Chondropterygii, otherwise called Cartilaginous 

 Fishes. 



ORDER I. 



ACANTHOPTERYGII.(l) 



The Acanthopterygii form the first and by far the most numerous 

 division of ordinary Fishes. They are recognized by the spines 

 which occupy the place of the first rays of their dorsal, or which 

 alone support the first fin of the back, where there are two; some- 



(1) Spiny-fins, 



