THE CONCEPT OF EVOLUTION 369 



discloses the lineage of horse and elephant, crocodile and 

 ammonite; it yields missing links to the sceptic; it shows 

 us above all that, as age succeeded age, there was an emer- 

 gence of nobler and nobler forms of life. 



We remember, too, how Darwin on his ' Beagle * voyage, 

 which discovered a new world, was struck by the simple 

 fact that the modern distribution of those strange survivals, 

 the sloths and armadillos, was centred round the burying- 

 ground of the huge majority of their race. And clinching 

 the whole argument, though we admit that it is only pre- 

 sumptive, there is the embryological evidence. The em- 

 bryos of reptiles, birds, and mammals travel in their devel- 

 opment for a considerable distance along the same road, 

 or along approximately parallel roads, before they diverge, 

 each on its own path; and in the making of organs there 

 is many a bend of the road very puzzling except on the 

 theory that the individual development is to some extent a 

 re-treading of the track which the race blazed in its evolu- 

 tion. What can be made of the gill-clefts in the region of 

 the neck in embryo reptiles, birds, and mammals, of no use 

 for breathing, of no use at all save the first, which becomes 

 the Eustachian tube, unless they be genuine relics of aquatic 

 ancestors breathing in fish-fashion ? 



The strength of the evolution-theory as a modal formula 

 of becoming is that it works well. It is a useful organon 

 of research. It clears things up and prompts discovery. 

 There is no other scientific formulation in the field. But 

 it is not without elements of weakness. In the first place, 

 we are remarkably ignorant in regard to the pedigree of 

 some of the most important types, such as backboned ani- 

 mals. This is not to be wondered at, because so many of 

 the great branches had begun to diverge from the genealogi- 



