THE GERM-PLASM THEORY 359 



(Fig. 13) ; and it can be observed that the three middle ones are the 

 longest, most sharply defined, and darkest, while those lying near 

 the tip and the base of the mimic leaf are shorter and often even 

 shadowy. On the left side the second lateral vein in particular 

 distinctly shows indentations indicative of the rings, inherited from 

 the ancestral forms, which surrounded the still visible eye-spots 

 (Aufi) ; the third lateral vein is quite indefinite and shadowy, but 

 nevertheless it runs exactly parallel to the first two, and thus heightens 

 the deceptive effect. We can thus distinguish older and more recent 

 elements in the marking — a proof of the slow and successive origin of 

 the picture. 



This is not reconcilable with the conception of a germ-plasm 



without primary constituents, however complex a mixture it may 



otherwise be. A substance which had to undergo thousands upon 



thousands of variations, arising from each other according to law 



and in the strictest succession, in order that it might become a definite 



organism, predetermined as to all its thousands of parts down to the 



most minute, cannot vary over and over again in its whole constitution 



without the consequences showing themselves in numerous, or indeed 



in all, the parts of the body. Such variations in the germ-plasm 



would be comparable to many successive deviations of a ship from 



her course, which, although the single ones would only cause a minimal 



deviation from the true course, would, when summed up in a voyage 



of some length, land the vessel at quite another coast than the one 



intended. If each individual adaptation of the species depended on 



a variation of the whole germ-plasm the wood Kallima would soon 



retain no resemV)lance to its ancestral form, the meadow species: 



yet we are acquainted with species of Kallima which do not show 



the special resemblance to a leaf, but, for instance, still exhibit the 



perfectly developed eye-spot of the ancestral form, and so forth. It 



follows, therefore, that the origin of the leaf-picture has not greatly 



influenced the general character of the species ; and the fact that the 



upper surface of the wings has remained the same in all the varieties 



is in itself enough to prove this. 



Since, then, the resemblance to a leaf cannot have arisen without 

 something in the germ-plasm varying, since the germ-plasm of a forest 

 Kallima and a meadow Kallima must be different in something, and 

 cannot be any more alike than the germ-plasm of a fantail-pigeon 

 and a carrier, there must be ' 2)rimary condituents' in the germ-plasm, 

 that is, vital units whose variation occasions the variation of definite 

 parts of the organism, and of these alone. 



It is on such considerations as these that my assumption, that 



z 2 



