[Illustration: FIG. 102. Brush and comb on the leg of a Bee (_Nomada_). _tib_, end of the tibia. _t^1_, first tarsal joint with the brush and its comb (_tak_). Between these and the tibial spine (_tisp_) with its lappet (_L_) the cross-section of an antenna (_At_) is indicated. Drawn from a preparation by Dr. Petrunkewitsch.] Instructive examples of the co-adaptation of several parts to a common action in organs which are not subject to the Lamarckian principle are afforded by the diverse arrangements for cleaning the antennæ the bearers of the smelling-organ which are so important to the life of insects (Fig. 102). Here even the adaptation of an indented area on the tibia of the anterior leg to the cylindrical form of the antenna which passes through it, is sometimes so striking (Fig. 102, _tak_) that it might be thought that it must have arisen through a gradual wearing out; yet this is impossible, since we have to do with hard dead chitinous surfaces, and moreover not with a solid mass, like a hone, which is worn down by the knife, but with a hollow, thin-walled tube. In ants, bees, and ichneumon-flies this minute, semi-circular indentation contains small, pointed, triangular saw-teeth, closely set like those of a comb (_tak_), and the apparatus is made usable by the fact that a firm spine (_tisp_), fused to the end of the tibia, overhangs the notch and presses the antenna towards it. In many species this spine is double, or it is furnished with a thin comb or lappet (Fig. 102, _L_), or with rows of teeth, or with short bristles; in short, it may be equipped in the most different ways. Not infrequently, as in wasps of the genera _Sphex_, _Scolia_, _Ammophila_, the spine itself is also bent in a semicircle on the surface directed towards the notch, and this may be effected in very different ways, either by a bending of the whole thickness of the spine, or by the presence of a comb which is concave on its inner surface. I should never come to an end if I were to enumerate all the remarkable details which may be found in the two main parts of this apparatus, and which show very clearly how essential a co-operation of the two is in fulfilling the function of cleaning the antennæ. This fitting together of the two main parts cannot have been brought about in accordance with the Lamarckian principle; the adaptation must therefore have come about in some other way.