DISTANT RELATIONS. 97 



place, which but for its commonness we 

 should regard as an almost incredible 

 marvel. You may there behold evolu- 

 tion actually illustrating the transformation 

 of life under your very eyes : you may- 

 watch a low type of gill-breathing gristly- 

 boned fish developing into the highest form 

 of lung-breathing terrestrial amphibian. Nay, 

 more you may almost discover the earliest 

 known ancestor of the whole vertebrate kind, 

 the first cousin of that once famous ascidian 

 larva, passing through all the upward stages 

 of existence which finally lead it to assume 

 the shape of a relatively perfect four-legged 

 animal. For the pond is swarming with fat 

 black tadpoles, which are just at this moment 

 losing their tails and developing their legs, 

 on the way to becoming fully formed frogs. 



The tadpole and the ascidian larva divide 

 between them the honour of preserving for 

 us in all its native simplicity the primitive 

 aspect of the vertebrate type. Beasts, birds, 

 reptiles, and fishes have all descended from 



ii 



