152 DARWINISM AND THE PROBLEMS OF LIFE 



imagine how the first land-animals could breathe, as 

 they would need an organ in some proportion to their 

 size. How could this be formed so quickly, seeing that 

 natural selection only builds up gradually from small 

 beginnings ? The mud - fishes remove the difficulty. 

 They afford most striking testimony to the theory of 

 evolution and natural selection, as they show that where 

 selection required a large organ as the beginning of the 

 lungs, it was forthcoming. It is well for us that in 

 the peculiar localities where land-animals arose some 

 of the transitional forms are still preserved ; the more 

 so as geology could give us no information on the 

 transformation, since soft parts are never fossilised.-^ 



The transition from the fishes to the amphibians is 

 seen, not only in the mud-fishes, but in the develop- 

 ment of every frog and salamander. The larvae of 

 the amphibians, when they issue from the egg, 

 breathe by gills, which closely resemble those of the 

 mud -fishes. In fact, the whole organisation of the 

 larvae is closer to that of the fish than to the adult 

 of the species they belong to. 



Even the adult amphibians very much resemble the 

 fishes ; all vertebrates must do so, in fact, if they 

 have descended from the fishes. We know how 

 natural selection, which must have brought about the 

 transformation, works. Variations in different organs 

 of the parent species, which are trifling at first, are 

 emphasised in the course of several generations. 



^ There are, however, recent experts who think the lungs were 

 formed, not from the swimming-bladder, but from sac-shaped folds 

 or outgrowths of the fore-part of the gut. 



