392 



ZOOLOGY. 



lary and intermaxillary bones are rudimentary, and the upper 

 jaw is formed essentially by the palatine bones. Sometimes 

 the gills are free at their edge, and sometimes fixed, and this 

 difference serves as a basis for their division into two groups, 

 namely, the chondropterygii with free branchiae, and those 

 with fixed branchiae ; and these latter are subdivided into two 

 others, the selaciens and the cyclostomes. 



Fig. 403. The Anchovy. 



502. The order of chondropterygii with free gills are 

 also called sturiones, because they have for their type the 

 sturgeon (sturio). It is composed of fishes in whose figure 

 there is nothing irregular (Fig. 405), and which have for the 

 most part the skin provided with large osseous plates dis- 

 posed in rows,* and the mouth toothless. 



Fig. 404. The Plaice. 



503. The chondropterygii with fixd gills have a re- 

 markable common character, which has already been de- 

 scribed. The gills are fixed at both edges, and instead of 

 having one opening by which the water escapes, there are 

 several, as many openings, in fact, as there are intervals 

 between the gills. The openings are almost always external, 

 nevertheless they terminate sometimes in a common canal, 



* In other words, a dermoid skeleton. E. K. 



