[Illustration: FIG. 156.—_Lepidasthenia elegans_ Gr., × 2, to illustrate colour-markings: the dark bands in the anterior part of the body occupy two elytriferous, and the intermediate segments. In the hinder region, where the elytra are in every third segment, this one is dark. _el._12, The twelfth elytron.] PROTECTIVE AND MIMETIC DEVICES.—From the point of view of "protection" in the evolutionist's sense of the word, we can {294}say but little. Protective resemblance there is undoubtedly amongst the Polynoids, for the scales of these forms resemble more or less closely the stones or sand amongst which they live; in the same species there is great variety in coloration. This protective habit is carried still further in the case of _Psammolyce_ by the attachment of sand grains to little cups on the elytra, so that the back of the animal is concealed. Certain commensals, such as _Polynoë arenicolae_, _P. pentactes_, are coloured so as to resemble their associates. In a few cases it is possible that the gills of Sabelliformia are protectively coloured; for in _Sabella pavonia_ they vary from a light yellowish tint to a deep violet-brown, and the dark markings on them are therefore more or less distinct. Spread out as the gills are in life, they are in many cases difficult to recognise; it is rather their movement as they are withdrawn that attracts one's attention to them, as the tubes of these worms frequently serve for the attachment of brownish seaweeds, to which the gills bear resemblance. But, as a matter of fact, little work has been done in this direction, and speculation on the matter without evidence is worthless. Many pelagic forms, being transparent, such as _Tomopteris_ and Alciopids, are no doubt protected by their lack of colour; yet these forms present brightly-coloured spots,—the light-producing organs in the parapodia of the former, and the large dark eyes of the latter. Semper[352] mentions a case of possible mimicry in a species of _Myxicola_ which lives in the clefts of a coral, _Cladocora_. The branchial funnel, when expanded, resembles very closely the expanded coral in size, colour, etc.; but he points out that the species occurs in other situations, where its colouring is not protective. Probably the "mimicry" is in other instances merely accidental. No doubt many Polychaetes may be "warningly coloured," but experimental evidence is incomplete. _Polycirrus aurantiacus_ is bright red, with orange tentacles; these worms were rejected by certain fish.[353] The animal has given up living in tubes as all its allies do, and it is the tentacles which appear to be distasteful to its enemies, for when irritated it coils itself up and wraps {295}itself round with its tentacles. Moreover, when the tentacles were cut off the fish did not reject the body of the worm. The tentacles are thus coloured in such a way that fish recognise them, and associate with the colour some distasteful property.