236 Prof. W. C. M‘Intosh on the 
they can dart upward very actively, nor will the explanation 
altogether suit the frog-fish (Lophtus). Some of the finest 
silvery bluish-green or yellowish touches of the short-spined 
Cottus are under the throat. The gorgeous colours of several 
of the British wrasses do not appear to be either for warning 
or protection, nor do they appear to be connected with Sexual 
Selection. Moreover, it may be asked if the white under 
surface of many terrestrial mammals has been acquired for 
the same reason, viz. rendering them invisible against the 
sky when viewed from beneath. In connexion with this 
explanation it has also to be remembered that the enemies of 
fishes do not always look at them from these points of view. 
Again, freshwater and marine fishes agree in regard to this 
coloration, and whilst the dark dorsal surface does aid in 
rendering the fishes obscure, the constant movement of the 
tail in streams makes them obvious enough. Besides certain 
silvery fishes with laterally compressed bodies are very 
conspicuous and the ventral edge is thin. Thus in the tidal 
pools in May young sand-eels of 4 inches swim in parallel 
ranks, conspicuous by their finely iridescent green backs and 
silvery sides, or sport amongst the fringing seaweeds like 
flashes of silvery heht in the sunshine. Such forms are no 
less conspicuous in the open sea—indeed, their only safety in 
this respect 1s immersion in sand. The dull biuish- black 
dorsum of the herring renders it less visible, but the approach 
of an enemy causes it to dart aside and expose the flashing 
silvery body. 
Prof. Moseley gives the instance of Antennarius, which 
coloured, like the gulf-weed (Sargassum), with spots of white 
to imitate the patches of Membranipora. Bright spots of white 
are common in young sea-scorpions, young lump-suckers, 
and others, but it would be difficult to draw a similar con- 
clusion. The adult shanny and the gunnel are certainly 
coloured in harmony with their surroundings, just as the 
upper surface of many flat-fishes is. The same may be said 
of other blennies. Mr. Garstang cites the black dorsal fin of 
the weever as a warning colour, lest it should be mistaken 
for the gurnard. The bold touches of black and other colours 
on the dorsal fins of other fishes are not, however, thus to be 
explained. 
Deep-sea fishes are black or white as if bleached (Moseley). 
On the other hand, the pelagic young of the conger (Lepto- 
cephalus) and of Plagusta are transparent. 
The pelagic young of some fishes, e. g. the skulpin, have 
the under surface darkly pigmented, yet its habits agree with 
those of its fellows which have the ‘same region translucent 
