458 PISCES. 



operculum in closing the gill-cavity in the higher fishes, and in this may be 

 developed the so-called branchiostegal rays. In the membrane joining the 

 two branches of the lower jaw may be certain large jugular plates. The 

 teeth of fishes need not engage our attention further than to notice that they 

 may be developed not only in the jaws and on the bones of the palate, but 

 likewise also on the tongue and the pharyngeal bones of the throat. The soft 

 internal parts must likewise be passed over almost without notice, although 

 it may be mentioned that whereas the heart generally comprises only two 

 chambers, in the lung- fishes it is furnished with three. The false gills, or 

 remnants of a former gill situated in front of the permanent pair, and re- 

 presented in the adult by a plexus of blood-vessels, are likewise too important 

 not to be named. Then, again, there are the spiracles of the sharks, which 

 are situated on the head, and are the openings of canals leading into the 

 pharynx, and representing the first visceral clefts of the embryo. It is like- 

 wise important to notice that certain fishes, such as the bichir of the Nile 

 and some of the lung-fishes, develop during the earlier stages of their existence 

 pectinate external gills, and thus serve to connect the class with the larval 

 forms of the Amphibia. As regards reproduction, it must suffice to say that 

 whereas most fishes lay eggs it may be of very small size, when they are 

 collectively known as roe, or comparatively large in certain kinds these 

 are retained within the body of the parent till hatched. The interesting 

 subject of distribution both in depth and in horizontal extent must be 

 passed over without mention. 



Excluding lampreys and lancelets, which are here assigned to distinct 

 classes, very different views have been entertained even by modern systematists 

 as to the proper classification of fishes. By Dr. Giinther the following scheme 

 for the existing forms was followed: even as late as 1880, viz. : 



Sub-class I. PAL^ICHTHYES. 



Order i. CHONDROPTERYGII. 



Section 1. Plagiostomata. Sharks and Rays. 



,, 2. Holocephala. Chimseroids. 

 Order ii. GANOIDEI. 



Section 1. Dipnoi. Lung-fishes. 

 ,, 2. Chondrostei. -Sturgeons. 

 ,, 3. Polypteroidei. Bichir. 

 ,, 4. Lepidosteoidei. Bony Pike, 

 5. Amioidei. Bow-fin, 

 Sub-class II. TELEOSTEI. Bony Fishes. 

 Order i. ACANTHOPTERYGII. 



ii. ACANTHOPTERYGII PHARYNGOGNATHI. 

 ,, iii. ANACANTHINI. 

 ,, iv. PHYSOSTOMI. 



,, V. LOPHOBRANCHII. 



,, vi. PLECTOGNATHI. 



The defects in this classification, are the wide separation of the Ganoidei 

 from the Teleostei, which, through the intervention of extinct forms, pass 

 completely into one another, and the association of the Chimseroids with the 

 Sharks and Rays to form a single subordinal group. 



A far better scheme is the one just published by Dr. Bashford Dean, which 

 is as follows : 



