MOLLUSCA OF PLYMOUTH SOUND. 175 



Several instances of pure " protective resemblance " to a fairly 

 fixed surrounding may be found in Giard, and also one whicli seems 

 to me to be a case of " mimicry " proper, namely, the resemblance 

 of Eolis papulosa to a contracted Sagartia parasitica, the dorsal 

 papillse of the former corresponding to the tentacles of the latter. 

 I have placed my remarks upon this most interesting case in my 

 notice of the species {infra). Giard has made a mistake in regard- 

 ing these cases of protective colouring as instances of a special 

 mimicry existing between the Nudibranchs and the particular species 

 which they affect for prey ; but emphasis ought not to be laid upon 

 this point, for (e. g.) Eolis papillosa not only preys upon Sagartia 

 parasitica, but attacks anemones generally. 



To what extent the colours of the smaller Eolids are explicable as 

 instances of this mimicry of Actinians, I do not feel prepared to say at 

 present. Wallace"^ thinks it probable that in some cases at least 

 they are " warning colours as a sign of inedibility." 



My own opinion is that the bright colours of the papillae of Eolids 

 in the majority of cases are serviceable in two ways. Their main 

 purpose is no doubt to warn enemies of the presence of disagreeable 

 qualities (e. g. nematocysts) . But from the bright colours being 

 generally confined to the papillae, which are well known to be detached 

 from the body with the greatest ease, and to be reformed to their 

 full size in two or three days, I think this arrangement must be 

 serviceable in directing the experimental attacks of young and inex- 

 perienced enemies to the non-vital papillae, and away from the vital, 

 inconspicuously coloured parts of the body. The enormous mortality 

 of Nudibranchst shows what would be the value in the struggle for 

 life of such a means of facilitating the education of enemies, while 

 giving the individuals themselves an additional chance of escape. 

 That butterflies often escape from the attacks of birds owing to the 

 conspicuousness and pi^ominence of their wings, is shown by the 

 many captures of individuals with mutilated wings which have been 

 recorded ; but in the case of Eolids such attacks of enemies (fishes 

 chiefly) at the same time give them the needful experience of the 

 unpalatable nature of their intended prey. J I have, however, ex- 

 periments in progress for the verification of these and other ideas as 

 to the value of colour in Nudibranchs and other groups of marine 

 animals. 



The ways in which colour probably serves as a protection through- 



* Darwinism, London, 1889, p. 266. 



t Cf. Darwin, Voyage of Beagle, 2nd edit., p. 245, note. 



X Since the above was in type Mr. Poulton has drawn my attention to his account of the 

 defensive value of " tussocks " in the larva of Orgyia (Trans. Ent. Soc, 1888, p. 589), 

 wliich I had quite overlooked. The analogy is remarkably striking. 



