222 Prof. W. C. M'Tntosh on the 



widest sense, so as to include birds) by Natural Selection and 

 Sexual Selection. Aforeover, the subject has been treated 

 under such heads as Pi-oteclive Resemhhince — that is, the tints 

 enable an animal to escape its enemies; Aggressive Resem- 

 hlaiice— 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 (7c)/o7'a</o?«, as exemplified by 

 conspicuous coloration in an animal havinp^ 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 throughout 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 iield responsible for the coloration 

 in the one case — that is, on land — it is difBcult 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) demersal, or forms which frequent the 

 bottom of the sea. This division is truly 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 |)erishing. 



Amongst the simplest marine animals colour is often 



