999 Prof. W. C. M‘Intosh on the 
widest sense, so as to include birds) by Natural Selection and 
Sexual Selection. Moreover, the subject has been treated 
under such heads as Protective Resemblance—that is, the tints 
enable an animal to escape its enemies; Aggressive Resem- 
blance— that is, the tints aid in capturing prey ; Protective 
Mimicry—a condition in which an animal is mistaken for 
another, and thus, as it were, lives on the reputation of 
another ; and, lastly, Warning Coloration, as exemplified by 
conspicuous coloration in an animal having an unpleasant 
attribute. Besides these subdivisions there are other cases in 
which special markings occur on an animal, apparently for 
recognition (for instance, the white tail of the rabbit) or for 
the purpose of diverting attack from a vital part (for example, 
wings of butterflies). In certain cases none of the foregoing 
causes exist, and these have therefore been termed cases of 
typical coloration. ‘The facts and arguments brought forward 
in support of the foregoing views will have the more weight 
if it be found that similar features are met with in the 
mammals, fishes, and invertebrates inhabiting the ocean. 
The sea offers a very different environment, however, from 
the land, since it is continuous thronghout its vast extent, so 
that it is possible for animals to pass from one region to 
another without the presence of those formidable barriers 
which, for example, restrict the land-mammals to certain 
isolated regions of the earth’s surface. Yet if Natural Selec- 
tion or Sexual Selection be held responsible for the coloration 
in the one case—that is, on land—it is difficult for either to 
escape similar responsibility in the marine forms. 
Again, it has to be remembered that light, aeration, and 
an abundant supply of food have a connexion with animal 
coloration, as may be observed in the subdued tones in the 
Nudibranchs and in anemones, either from deep or shallow 
water, after confinement. 
In dealing with the coloration of marine animals under the 
several classes it. will suffice to divide them severally into 
two great groups, a classification which has been of service on 
former occasions, viz.: (1) pelagic, that is, swimming or floating 
animals, and (2) demers al, or forms which frequent the 
bottom of the sea. This division is tr uly one of convenience, 
since the two groups are closely connected, some in their 
young state being pelagic whilst they are demersal in their 
adult; others, again, though perhaps springing from pelagic 
young, generally live on the bottom till they put on their 
nuptial dress, when they swim freely in the water, scattering 
their eggs all around and then perishing. 
2) 
c 
Amongst the simplest marine animals colour is often 
