3 2 ° 
FISHES. 
Coloration. 
Soft Parts. 
they are welded to the underlying bone or cartilage by a broad basis; but, as in 
the saw-fishes, they may be emplanted in distinct sockets. Usually the coating of 
enamel is very thin; and the ivory, or dentine, is more vascular than in the other 
classes. In rare instances the ivory may be penetrated by branching prolongations 
from the central pulp-cavity, as well as by similar infoldings from the exterior, 
thus producing a structure similar to that obtaining in those of the primeval 
salamanders. As a general rule the teeth are being constantly renewed through¬ 
out life, but in a few instances a single set persists. 
In beauty, variety, and changeability, the colours of fishes 
cannot be exceeded by those of any of the other vertebrate classes; 
metallic tints and almost all the colours of the rainbow being very commonly 
displayed; while the beauty of the coloration is often enhanced by the rapid 
changes it undergoes. In many cases the coloration is of a protective nature. 
An example of this is afforded by the colouring of the upper surface of many 
flat-fishes, such as flounders, which exactly harmonises with the tints of the sea- 
bottom on which they dwell; while another equally marked instance presents 
itself in the case of so-called pelagic fishes, like the mackerels and flying-fish, 
which live near the surface of the sea, and have the under-parts silvery white, and 
the back mottled with dark green and black. When viewed from below against 
the light sky such a fish is practically invisible, while it is equally inconspicuous 
when seen from above among the dark waters. 
The body of fishes is made up of a great lateral muscle on each side, 
divided into a number of segments corresponding with the vertebrae, 
and also separated into a dorsal and ventral moiety by a median longitudinal 
groove. On its surface the lateral muscle is marked by a number of white zigzag 
stripes, generally forming three angles, of which the middle one is directed 
forwards; these stripes being formed by the edges of the tendinous divisions 
between the segments. Generally the muscles are glistening white in colour; 
but in some instances they are “ salmon-coloured,” this tint being due to the 
colouring matter of the crustaceans on which such fish subsist, which is turned 
red by the action of the digestive fluids in the same manner as by boiling. The 
electric organs possessed by certain fishes are considered to be probably formed 
from specially developed muscles. With regard to the brain, it will suffice to say 
that it is of an exceedingly low type; and that the ear lacks the tympanum and 
tympanic cavity of the higher classes. In the bony fishes there occurs at the 
base of the brain-cavity a sac, often divided into two unequal-sized chambers, and 
each of which contains an ear bone, or otolith, of very dense structure. These 
otoliths, which are very constant in form in the different groups, frequently have 
scalloped margins and groove-like markings, formed by the ramifications of the 
auditory nerve. The tongue is frequently absent, and if present is of very simple 
structure and incapable of protrusion; and since fishes generally bolt their food 
without mastication, it is probable that they have little, if any, sense of taste. 
With regard to the digestive organs, it will suffice to mention that in the sharks, 
rays, and chimseroids the intestine for a large portion of its length is provided 
with a spiral valve, a similar structure occurring in the ichthyosaurian reptiles. 
The gills of sharks, rays, and chimseroids are contained in pouches, usually 
