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 
Thoracier 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 Apodes 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 grouping the smaller divisions, and for the determination of species ; 
moreover the dorsal and anal rays or spines generally correspond to the 
number of vertebre 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 other 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 cecus) 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 operculum, but this name is only applied 
to the hind margin. In most Teleosteans there is a semicircular bone in 
