152 THE LESSON OF EVOLUTION 



individual an advantage over another. Neither can 

 it matter in the struggle for life whether the nervure 

 in the wing of an insect branches once or twice. 

 Again, can we suppose that slight differences in the 

 number or shape of the teeth in snails have any 

 adaptive value ? Or take the shape of the spicules in 

 sponges, or the small differences in the leaves of 

 ferns and mosses, or the various patterns of orna- 

 mentation on the valves of diatoms : can all or any 

 of these characters be explained by the law of utility ? 

 No one, I believe, is at present prepared to maintain 

 that they can. 



But it will be as well to give a few special illus- 

 trations. The Radiolarians are minute, microscopic 

 animals, whose soft body is supported by an internal 

 siliceous cage, or skeleton, of great variety 

 of form. Now these different forms cannot be cor- 

 related with each other, for each species has its own ; 

 and they cannot be recognition-marks. The skele- 

 ton, of course, is useful to the animal as a support, 

 and as a defence against enemies. But several of the 

 forms which we find in living Badiolarians we also 

 find in Radiolarians which lived near the commence- 

 ment of the Palaeozoic era. During almost the 

 whole history of life on the earth these different 

 forms of skeleton have been competing with each 

 other. During this competition many other forms 

 of skeleton came into existence ; but they did not 

 vanquish the old ones ; all lived and multiplied 

 alongside each other, without any one obtaining the 

 victory. Obviously, the particular form of the 

 skeleton cannot give any advantage, and cannot 

 therefore be due to natural selection. 



