OF EVOLUTION. 13 



cold-blooded, water-inhabiting animals, breathing 

 by means of ills, having but two chambers to the 

 heart, and rejoicing in a purely systemic circula- 

 tion i. e., the arterialized or oxygenated blood 

 instead of being returned to the heart before being 

 finally distributed, is carried directly from the gills 

 to the different parts of the body. The body, 

 moreover, is provided with fins, which fins are sup- 

 ported by fin-rays. When we compare this general 

 structure with that of an amphibian, such as a sal- 

 amander or frog, we naturally find much difference. 

 The frog breathes by means of lungs, is largely an 

 inhabitant of the land, has three chambers to its 

 heart, has a true pulmonary circulation the blood 

 being first returned from the lungs to the heart 

 before it is finally distributed and the body is des- 

 titute of fins and supporting fin-rays, Thus, there 

 would appear to be but little connection between 

 these two classes of animals. When, however, we 

 inquire into the early history of the frog we find a 

 very close connection, and one that proves the 

 young frog to be more of a fish than anything else. 



