no CHARLES DARWIN 



obscured and blurred in its outline, of the common 

 progenitor of a whole great class of plants or animals. 



Finally, classification points in the same way to the 

 affiliation of all existing genera and species upon certain 

 early divergent ancestors. The whole scheme of the 

 biological system, as initiated by Linnaeus and improved 

 by Cuvier, Jussieu, De Candolle, and their successors, 

 is essentially that of a genealogical tree. The prime 

 central vertebrate ancestor to take the case of the 

 creatures most familiar to the general reader appears 

 to have been an animal not unlike the existing lancelet, 

 a mud-haunting, cartilaginous, undeveloped fish, whose 

 main lineaments are also embryologically preserved for 

 us in the ascidian larva and the common tadpole. 

 From this early common centre have been developed, 

 apparently, in one direction the fishes, and in another 

 the amphibian tribes of frogs, newts, salamanders, and 

 axolotls. From an early amphibian, again, the common 

 ancestor of birds, reptiles, and mammals seems to have 

 diverged : the intermediate links between bird and 

 reptile being faintly traced among the extinct deino- 

 saurians and the archseopteryx, some years subsequently 

 to the first appearance of the ' Origin of Species ; ' while 

 the ornithorhyncus, which to some extent connects the 

 mammals, and especially the marsupials, with the lower 

 egg-laying types of vertebrate, was already well-known 

 and thoroughly studied before the publication of 

 Darwin's great work. Throughout, the indications 

 given by all the chief tribes of animals and plants point 

 back to slow descent and divergence from common 

 ancestors ; and all the subsequent course of palseonto- 

 logical research has supplied us rapidly, one after 



