84 



THE EVOLUTION THEORY 



is thus possible that co-adaptation of at least two parts may take 

 place even when the hypothetical Lamarckian principle is altogether 

 excluded. 



When I say that we have here a case of two parts adapted to 

 each other, that is, strictly speaking, understating the case, for, in 

 the crickets and locusts, for instance, there is a whole series of peg- 

 like chitinous papillas (Fig. 86), the so-called ' bridge,' each of which 

 must have arisen by itself through variation of the corresponding spot 



of skin. At least I can see no ground 

 for the assumption that the chitinous 

 surfaces on which the ' bridge ' is now 

 placed would necessarily, from inter- 

 nal reasons, have varied precisely in 

 the line of the bridge as it has done. 



Instructive examples of the co- 

 adaptation of several parts to a 

 common action in organs which are 

 not subject to the Lamarckian prin- 

 ciple are afforded by the diverse 

 arrangements for cleaning the an- 

 tennae, 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 



Fig. 102. 



Brush and comb on the 

 leg of a Bee (Nomada). tib, end of 

 the tibia, i', first tarsal joint with the 

 brush and its comb {tak). Between 

 these and the tibial spine {tisp) with 

 its lappet (i) the cross-section of an 

 antenna {At) is indicated. Drawn from 

 a preparation by Dr. Petrunkewitsch. 



mip-ht be thousrht that it must have 



c5 O 



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 {tah), 

 and the apparatus is made usable by the fact that a firm spine (fi'y/)), 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, X), or with rows of teeth, or 

 with short bristles ; in short, it may be equipped in the most different 



