314 PHILOSOPHY OF ZOOLOGY. 



are situated the anal fins, which vary in number and shape 

 according to the species. Between the anus and throat are 

 placed the ventral fins. When they do exist, they never 

 exceed two in number, and are parallel to each other. The 

 pectoral Jins are usually two in number, and are placed 

 on each side, a short way behind the gill opening. By 

 Linnaeus and others, the ventral fins are considered as ana- 

 logous to the feet of quadrupeds, and the characters fur- 

 nished by their position are employed as the basis of his 

 classification. Those fishes which are destitute of ventral 

 fins, are termed, in his system, apodal ; those which have 

 the ventral fins placed nearer to tlie anterior extremity 

 than the pectoral fins, are termed jugular ; those having 

 the ventral fins on the belly, immediately below the pectoral, 

 he calls tlioracic, and when the ventral fins are placed be- 

 hind the pectoral fins, they are termed abdominal. These 

 distinctions are of great importance in an artificial system, 

 and may be employed with success in the inferior divisions 

 of a natural one. 



The structure of the fins of fishes has long occupied the 

 attention of naturalists. In general, these oi'gans consist 

 of numerous jointed rays, which are subdivided at their ex- 

 tremities. These are covered on each side by the common 

 integuments, which form, in some instances, soft fibres pro- 

 jecting beyond the rays. These fins, with articulated rays, 

 were considered, by the older ichthyologists, as furnishing 

 characters for arrangement, of great importance, and are 

 still highly valued by many naturalists. Fishes possess- 

 ing these roft rays, are termed mcdacopterygii. Besides 

 these articulated rays, there exist in the fins of some fishes 

 one or more rays, made up of a single bony piece, envelop- 

 ed like the former, by a common membrane. Some fishes 

 have one or more lins consisting entirely of these bony rays. 

 Fishes with such rays arc termed acanthopterugii. In 



