122 ORDER OF SELACIIII. 



sturgeons : they are remarkable for an enormous prolongation 

 of the muzzle, to which its wide borders give the figure of a leaf. 

 The mouth is well cleft, and furnished with numerous small 

 teeth. 



6. The Chimceras form a connecting link between the preceding 

 and the sharks, which they resemble in the general form of the 

 body. 



CHONDROPTERYGII BRANCHIIS FIXIS. 



7. The Chondropterygians with fixed branchiae, which form 

 the two orders of Selachii and Cyclostomi, possess a very re- 

 markable character in the arrangement of their respiratory 

 apparatus, which is common to them all. Instead of having the 

 branchiae free on the external edge, and suspended in a common 

 cavity, from which the water escapes by a single opening, they 

 have them, on the contrary, adherent to the integuments, so that, 

 for the escape of the water that laves them, there is required as 

 many openings as there are intervals betwixt them ; sometimes, 

 however, they empty into a common canal, which serves to 

 transmit the water externally ; and their cartilaginous arches, often 

 suspended in the flesh, are placed opposite to the external edges 

 of the branchiae. In other respects these fishes differ very much 

 from each other, and are divided into two orders, according as 

 they are provided with moveable jaws of the ordinary form, or 

 according as these organs are solidly united into an irnmove- 

 able ring, only suited for suction. The first are the Selachii, and 

 the second the Cyclostomi. 



ORDER OF SELACHI1. 



8. This order comprises the greatest number of cartilaginous 

 fishes, Rays and Sharks, for example. Their external form 

 varies ; they have pectoral fins ; ventral fins situate on the 

 abdomen near the anus ; five branchial openings in the form of 

 slits, on each side of the neck, or on its inferior face, and the jaws 

 are armed with teeth. In a great many of these fishes, there is 

 on the upper surface of the head, two openings, called vents, or 

 spiracles, which lead to the branchiae, and serve to carry off the 

 water, necessary to respiration, when the throat of the animal is 



6. What are Chimseras ? 



7. What are the characters of Chondropterygians with, fixed branchiee ? 

 What are the peculiarities of their branchiae ? 



8. How is the order of Selachii characterised ? 



