CHAPTER XXV. 



OEDEES OF FISHES. 



THE number of different kinds of fishes is so enormous that 

 nothing further will be attempted than merely to give an out- 

 line of the leading peculiarities which distinguish the different 

 orders. The classification here adopted is the one proposed 

 by Prof. Huxley, who divides the class Pisces into the follow- 

 ing six orders : 



1. Pharyngobranchii. 



2. Marsipobranchii. 



3. Teleostei. 



4. Ganoidei. 



5. ElasmobranchiL 



6. Dipnoi. 



OEDEE I. PHAEYNGOBEAKCHII (Gr. pliarugx, the upper part 

 of the gullet, and bragchia, gills). This order of fishes in- 

 cludes only a single animal, the anomalous Amphioxus, or 

 Lancelot, the organization of which differs in almost all its 

 important points from that of all the other members of the 

 class. In fact, the Lancelet presents us with the lowest type 

 of organization as yet known in the Vertebrata. The Lance- 

 let is an extraordinary little fish, from one and a half to two 

 inches long, which burrows in sand-banks in various seas, but 

 is especially abundant in the Mediterranean. The body is 

 lanceolate in shape, and is provided with a narrow membra- 

 nous border, of the nature of a median fin, which runs along 

 the whole of the dorsal and a portion of the ventral surface, 

 and expands at the tail to form a lancet-shaped caudal fin. 

 There are no true " paired " fins, representing the fore and 

 hind limbs. The mouth is a longitudinal fissure, placed at the 

 front of the head, and completely destitute of jaws, but sur- 



