i 4 THE GEOLOGICAL EVIDENCES 



The familiar tadpole or fish-like form is an inhabit- 

 ant of water, and like the fish it breathes water by 

 means of gills; it has but two partitions to its heart, 

 a non-pulmonary circulation precisely like that 

 of the fish, and the body provided with fins, which 

 are, however, destitute of fin-rays. 



Leaving out certain differences in the osteolog- 

 ical structure of the cranium, we might indeed say 

 that almost the only striking character separating 

 this larval amphibian from the fishes is the absence 

 of fin-rays ; but in whatever way we look upon it, 

 the creature is much more a fish than anything 

 else, and differs less from certain fishes than these 

 do from each other. So that to all intents and pur- 

 poses the frog is a dual creature a fish in its young 

 stage and something else afterwards. Why then, 

 it might be asked, separate the amphibians from 

 the fishes at all? The master mind of Professor 

 Huxley has solved this question. The fishes and 

 amphibians are but sub-groups of a single division, 

 known to naturalists as the Ichthyopsida. I 

 have thus far indicated to you only a one-sided 



