FISH AND FISHERIES. 7 



mullet, herring, pipe-fish. When the ventral fins were situated on the 

 breast or nearly under the pectorals, they formed an order called 

 Thoracici or breast-fish, including dolphins, goby, dory, sole, wrasse, 

 perch, mackerel, gurnard, flying-fish ; and if the ventral fins were 

 situated under the throat the fishes were included in an order called 

 Jugulares or throat-fish, including cod, whiting, hake, blenny. Fish 

 without ventral fins were classed together as Abodes or footless. 



It will be seen that this arrangement, however convenient in one re- 

 spect, took no notice of the resemblances or differences of fishes in many 

 other respects ; and thus its groups were of the most mixed description. 

 For this reason it was called artificial, because it gave no knowledge of 

 the harmonious plan which prevails throughout nature. 



But while the position of the fins is of little value in classification, the 

 number of rays or spines in the ventral fins is of the greatest importance 

 in grou];)ing the smaller divisions, and for the determination of species ; 

 moreover the dorsal and anal rays or spines generally correspond to the 

 number of vertebrae in a certain portion of the backbone ; they form 

 therefore constant and unvarying characters by which species, genera, 

 and even families may be distinguished. The only exception to this rule 

 is that if the number of spines is very great a proportionately wide 

 margin must be allowed for variation (Giinther). The number of 

 pectoral or caudal rays is rarely of any importance. 



A few words more will be necessary to describe certain otlier parts of 

 fishes which are referred to in systems of classification. The eye is taken 

 as a point for dividing the head into the ante-orbital and post-orbital 

 portions. The organ is proportionately larger in most fishes than in 

 other vertebrates. Fishes with very large eyes are either nocturnal in 

 their habits or live at depths in the ocean to which but little light pene- 

 trates. Where scarcely any light is found the fishes have small or rudi- 

 mentary eyes, or the eyes are hidden under the skin. Fishes inhabiting 

 muddy places have small eyes. The Hon. W. Macleay has described a fish 

 from North Australia {Polynemus ccecus) which has a thick membrane 

 over the eyes, rendering it if not blind at least only capable of perceiving 

 light. It was found at the entrance of muddy rivers. This is not an 

 uncommon feature in the genus Polynemus all of which have long feelers 

 under the pectoral fins to take the place of eyes. 



The space between the eyes is called the inter-orbital space or fore- 

 head ; that beneath them is called the sub-orbital or infra-orbital. In 

 the ante-orbital space are placed the mouth and nostrils. The mouth is 

 formed by the maxillary or inter-maxillary bones or by the inter-maxil- 

 lary only in the upper jaw, and by the mandibulary bone in the lower. 

 These bones are sometimes bare, but folds of skin, forming lips, are often 

 added. ■ To the jaws are added the only weapons of attack which fishes 

 have. Sometimes skin appendages called barbels are attached to both 

 jaws, which generally are organs of touch. In most fishes the nostrils 

 are a double opening on each side of the upper surface of the snout; 

 they lead into a shallow groove, and in only one family perforate the 

 palate (the Myxinoids). In sharks and rays they are underneath the 

 snout, and more or less confluent. 



The gill-cover is called the opercuhcm, but this name is only applied 

 to the hind margin. In most Teleosteans there is a semicircular bone in 



