DISHARMONIES AND OTHER SHADOWS 575 



Pterodactyls that could fly, are such lost races, not continued 

 into other stocks, wonderful achievements, but lacking in 

 plasticity. As the palaeontologist Marsh said, the epitaph of 

 the Iguanodon might be, " I and my race died of over- 

 specialisation ", and he might have added * and stupidity ', 

 for there was not in these ancient giants the intellectual re- 

 sourcefulness which we see in the still more specialised mod- 

 ern birds who can adapt themselves to many a drastic change. 

 We must admit that the extinction of splendidly perfect 

 types raises strange thoughts. What can one say save that 

 every art is limited by its medium, and that here the medium 

 is twofold, the inorganic and the organic? The inorganic 

 world is the grindstone on which life has been whetted, and 

 it cannot become a soft cushion. An environment without 

 vicissitudes might have meant an unprogressive fauna and 

 flora of jellyfishes and seaweeds. Against the callousness 

 of the inorganic domain, moreover, we should remember, 

 though with dread of a circular argument, the other fact that 

 the physical conditions are singularly well suited to be a home 

 of living creatures. Moreover, the lack of plasticity in or- 

 ganic structure is the minus side of that stability which 

 marks the journey-work of millennia. What is stable cannot 

 also be labile. Furthermore, some of the gains of lost races 

 may be continued on collateral lines. 



3. Imperfect Adaptations. 



Another shadow is the existence of imperfect adaptations. 

 These are of two kinds. First, there are established arrange- 

 ments which work well on the whole, but now and again 

 break down or miss the mark, as is the case with tropisms 

 and instincts that are in ninety-nine situations adaptive, but 

 in the hundredth suicidal. The crepuscular moth, unaccus- 



