TRANSMISSIBILITY OF FUNCTIONAL MODIFICATIONS 



85 



ways. Not infrequently, as in wasps of the genera Sphex, Scolia, 

 AmTnojMla, 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 antennse. 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. 



The same thing is shown by the legs and other appendages of 

 insects and crustaceans, 



which are adapted for Oc/i 



the most diverse func- 

 tions, and the individual 

 sections of which must 

 be correlated if thef unc- 

 tion is to be possible. 

 Let us consider only 

 the claw structures in 

 crustaceans and scor- 

 pions. Here, too, it Yig. 103. Claw (Sch) on the leg of a 'Beach-fly,' an 



^PPm^ as if the out- Amphipod Crustacean (Orchestia). I, II, the two first 

 seems as 11 tne out _^^^ ^^^^ ^^^ j^^^^. ^^^^^^ ^^ ^^^^ ^j.^^^^ ^ non-mobile 



growth of the last joint prolonsjatlon of the penultimate joint. oA, the upper 



n ,-, 1 1 • -u -(-• blade of the claw, the movable last joint ; the tubercles 



of the leg, which tunc- ^^^^i^.^entations of the two blades fit one another. After 



tions as the arm of the F. Miiiler. 

 claw, must have arisen 



as a direct effect of use, through the pressure of an object held 

 fast by the last joint, the movable half of the claw. Frequently, 

 moreover, tooth-like protuberances occur on the fixed blade of the 

 claw (Fig. 103). But how could these have arisen as a direct effect 

 of pressure, since they are always preformed during the soft state of 

 the appendage before use, and are only made use of after it is fully 

 hardened. The soft crustaceans, the so-called 'butter-crabs' which 

 have just cast their shells, creep carefully away and avoid using their 

 limbs until they have become hard again. Here, too, we have the 

 co-adaptation of two parts which vary independently, and which cannot 

 be affected by the Lamarckian principle. 



But the appendages furnish more complex examples of mutual 

 adaptation. Thus the individual sections of the anterior leg of the 



