164 FISHES CHAP. 
complex system of branching grooves or of deeply-seated and 
externally inconspicuous canals. The course of the lateral line 
can, as a rule, readily be detected by the naked eye, and, even 
when not otherwise distinguishable, may be traced by the series 
of simple or multiple pores through which, at intervals, the 
canal communicates with the exterior (Fig. 93, A), and often also, 
in the trunk and tail, by a band of coloration different to that of 
the rest of the body. 
Coloration. 
Contrary to popular opinion, it may be doubted if any | 
animals, even Insects or Birds, can vie with lhving Fishes in the 
briluaney and changeability of their colours. The nature of 
their habitat, the rapid fading of the natural tints after death, 
and the fact that museum specimens, however carefully pre- 
served, afford but a ghostly resemblance to the colours of the living 
animal, account, no doubt, for much of the prevalent ignorance 
of the extraordinary extent to which colour-development may 
proceed in a considerable number of Fishes. Like the generality 
of northern forms of life, the Fishes of our own seas, rivers and 
lakes, are less conspicuous for vivid and striking coloration than 
those of tropical or subtropical climes, although such familiar 
Teleostean Fishes of our seas and fresh waters as the Mackerel, the 
Salmon and Trout, the males of the Stickleback and Dragonet, 
some of the Gurnards (Triglidae) and Wrasses (Labridae), the 
Opah or King-Fish (Lampris luna), and many others, are notable 
exceptions. Brilliancy of coloration is most conspicuous in the 
Teleostei: in nearly all other Fishes the colours are more uniform, 
usually sober and often sombre, with no more variety than is 
afforded by the presence of dark spots or bands on a lighter 
ground, or vice versd, or by the lighter colour of the ventral as 
compared with the dorsal surface. In Teleosts all the resources 
of colour-formation, pigmentation, reflection, and iridescence 
through optical interference, in diverse combinations, are employed 
in the production of the various tints, while the dominant ground 
colour is often diversified by the presence of stripes, bands or 
bars, longitudinal or transverse, or of spots of different hues, 
frequently arranged in striking and intricate patterns. 
The possibilities of coloration in these Fishes may be briefly 
illustrated by a few examples :— 
