EVOLUTION 1077 



ing. The process of moulting or ecdysis in crustaceans is hazardous 

 and fatiguing, sometimes maiming and occasionally fatal ; but these 

 disadvantages are trivial compared with the advantages of the firm 

 cuticular exoskeleton that forms a resistant armour and makes the 

 jointed legs very effective levers and weapons. 



There is an obvious danger lest a strong urge carry the organism 

 too far; thus the over-sexed toads may be drow^ned by their sexual 

 embrace, and the over-eager drakes may drown the duck in their 

 orgasm. It is readily intelligible that an animal may suffer from 

 the defects of its qualities. 



In other cases the apparent mis-adaptation is due to some unusual 

 change in the normal conditions of a tropistic or instinctive routine. 

 Thus the moth flies into the artificial stimulus of the candle, and 

 the lemmings sometimes swim with fatal persistence out to sea. 



No doubt there are some difficult cases, but they are few and far 

 between. A tree may fall when its exposure to the breeze becomes 

 too great for the roots to stand, but the wonder is that this does 

 not happen oftener. One must also ask how far the disproportion is 

 due to artificial conditions of growth in plantations. In short, the 

 evidence of "dysteleology", as Haeckel called it, is not convincing. 



ORIGIN OF ADAPTATIONS.— This problem is but a special 

 case of organic evolution in general, and we refer to the section 

 dealing with the Factors of Evolution. What is said here must be 

 very brief. 



There are two main theories in the field — direct and indirect 

 adaptation, using the word here to denote the process not the result. 

 According to Lamarck's theory of direct adaptation, there has been 

 a cumulative inheritance of individual modifications which arise 

 under the influence of what he called besoin et desir, not neces- 

 sarily so conscious as need and desire — and hence now called 

 "organic urge", or libido, and by Bergson elan vital. There is as 

 yet a paucity of positive evidence in support of this interpretation, 

 plausible as it seems to be. Two obvious difficulties occur to the 

 critic, (i) that hard chitinous structures like the instruments and 

 weapons of insects are non-cellular and non-protoplasmic, and could 

 not enregister the results of individual use and disuse ; and (2) that 

 some structures, such as the egg-opener in birds, or the often 

 intricate coupling organs of some male insects, like dragon-flies, 

 are used only once in a lifetime. But while the direct origin of an 

 adaptation is excluded in cases like this, it does not follow that other 

 adaptations may not have arisen in this way, especially in the case 

 of structures much used through the organism's lifetime. 



The Darwinian theory is that adaptations arise by the selection 

 of germinal and heritable variations which have survival value by 

 making their possessors appreciably fitter in the struggle for exist- 



