338 TRANSACTIONS, NATURAL HISTORY SOCIETY OF GLASGOW. 
young Ooal-fish or Saithe (Gadus virens, Linn.). As is well 
known, this fish is so named from its dark flesh and generally 
dingy appearance in the adult stage. But a shoal of young Saithe, 
two or more inches in length, from the tangle area, are wonderfully 
richly coloured, and, in many cases, are beautiful creatures. 
Still more is this the case with the young Lythe or Pollock 
(Gadus pollachius, Linn.), a greater liver in and frequenter of 
tangle-covered areas than its congener. These are sometimes very 
gay indeed, and yet do not retain their external gaiety of appear- 
ance into the adult stage. If the Rock-cod were to live upon these 
bright youngsters, as they do to some extent, no doubt they might 
be influenced themselves, and the pigment absorbed might have its 
effect. Another, but less-known, member of the family—the little 
Five-bearded Rockling (Jotella mustela (Linn.) )—that dwells in- 
shore and amongst the tangle, becomes so much of a golden-syrup 
colour at times as to vie with the Gold Carp itself in glory, but 
removed from its locality it very soon loses this. This colouring, 
depending upon locality and surroundings, therefore, cannot be 
proved to be the result of any isolated cause, and may arise from 
a sudden “sentiment ;” from the action of light as reflected from 
the rich tints around ; from feeding, originally springing from the 
same vegetable colouring ; or from what may be termed the third 
cause of colour, namely, protective colouring. 
It is impossible to cover in any such paper the whole ground of the 
marvellous variations—apparently purely protective—in colour 
and in form that take place in fishes as in other departments of 
nature, but only to refer to it in so far as it comes specially within 
our argument. Certain broad facts tend to protection, and yet 
may not be in any degree dependent upon the effort after conceal- 
ment, or even accentuated by its tendency towards the security of 
the species. Thus, if we look down ona shoal of Herring (Clupea 
harengus, Linn.) or Mackerel (Scomber scomber, Linn.), they so 
assimilate to the greenish-blue of the sea that no better colour 
could be devised to ensure them against even the keen sight of 
sea-fowl. Again, predatory fish looking up from under such a 
shoal will only meet the colourless under-surface between them 
and the entering light. But it can scarcely be supposed that in 
either case any real advantage thereby accrues either to the species 
or individuals, The deepest colour is on the surface, where the light 
