OCEANOGRAPHY, BIONOMICS, AND AQUICULTURE. 447 



the two most powerful factors in influencing an animal. We can study 

 mimicry, and test theories of protective and warning coloration. 



The explanations given by these theories of the varied forms and 

 colors of animals were first applied by such leaders in our science as 

 Bates, Wallace, and Darwin, chiefly to insects and birds, but Lave 

 lately been extended, by the investigations of Giard, Garstang, Clubb, 

 and others, to the case of marine animals. I may mention very briefly 

 one or two examples. Amongst the Nudibranchiate Mollusca — familiar 

 animals around most parts of our British coasts — we meet with various 

 forms which are edible, and, so far as we know, unprotected by any 

 defensive or offensive apparatus. Such forms are usually shaped or 

 colored so as to resemble more or less their surroundings, and so 

 become inconspicuous in their natural haunts. Dendronotus arbores- 

 cens, one of the largest and most handsome of our British Nudi- 

 branchs, is such a case. The large, branched processes on its back, 

 and its rich purple-brown and yellow markings, tone in so well with 

 the masses of brown and yellow zoophytes and purplish red seaweeds, 

 amongst which we usually find Dendronotus, that it becomes very com. 

 pletely protected from observation 5 and, as I know from my own expe- 

 rience, the practiced eye of the naturalist may fail to detect it lying 

 before him in the tangled forests of a shore pool. 



Other Nudibranchs, however, belonging to the genus Eolis, for exam- 

 ple, are colored in such a brilliant and seemingly crude manner that 

 they do not tone in with any natural surroundings, and so are always 

 conspicuous. They are active in their habits, and seem rather to court 

 observation than to shun it. When we remember that such species of 

 Eolis are protected by the numerous stinging cells in the cnidophorous 

 sacs placed on the tips of all the dorsal processes, and that they do 

 not seem to be eaten by other animals, we have at once an explanation 

 of their fearless habits and of their conspicuous appearance. The 

 brilliant colors are in this case of a warning nature, for the purpose of 

 rendering the animal provided with the stinging cells noticeable and 

 recognizable. But it must be remembered that in a museum jar, or in 

 a laboratory dish, or as an illustration in a book or on the wall, Den- 

 dronotus is quite as conspicuous and striking an animal as Eolis. In 

 order to interpret correctly the effect of their forms and colors we 

 must see them alive and at home, and we must experiment upon their 

 edibility or otherwise in the tanks of our biological stations. 1 



Let me give you one more example of a somewhat different kind. 

 The soft, unprotected mollusk, Lamellaria perspicua, is not uncommonly 

 found associated (as Giard first pointed out) with colonies of the 

 compound Ascidian Leptoclinum macnlatum, and in these cases the 

 Lamellaria is found to be eating the Leptoclinum, and lies in a slight 

 cavity which it has excavated in the Ascidian colony, so as to be about 



•See my experiments on fishes with Nnrtihranchs, in Trans. Biol. Soc, Liverpool, 

 Vol. IV, p. 150; and Nature for June 26, 1890. 



