GRADATION AMONG ANIMALS. 99 



ers, who wrought their myriad lives into the solid 

 crust of our globe then, as their successors do now, 

 we find a peculiar kind of Polyp Coral. These 

 old Corals have their representatives among the 

 present Polyps, and from their structure they 

 are placed lowest in their class, while the embry- 

 ological development of the higher ones recalls 

 in the younger condition of the germ the same 

 character. I might multiply examples, and 

 draw equally striking illustrations from the other 

 classes ; and though these correspondences can- 

 not be fully established while our knowledge of 

 the embryological growth of animals is so scanty, 

 and there remain so many gaps in our informa- 

 tion about their geological succession, yet wher- 

 ever we have been able to trace the connected 

 history of any group of animals in time, and to 

 compare it with the history of their embryologi- 

 cal development and their structural relations as 

 they exist to-day, the correspondence is found to 

 l>e so complete as to justify us in the belief that 

 it will not fail in other instances. 



I may add that a gradation of exactly the same 

 character controls the geographical distribution 

 of animals over the surface of the globe. Here 

 again I must beg my readers to take much of the 

 evidence, which, if expanded, would fill many 

 volumes, for granted, since it would be entirely 

 inappropriate here. But 1 may briefly state thai 



