1 82 SCIENCE SKETCHES. 



We name and arrange them arbitrarily in default 

 of means of reconstructing the whole tree in ac- 

 cordance with Nature's ramifications." Among- 

 Dareste's eels we may have one species, or four, or 

 forty, as our collection may be deficient in con- 

 necting forms, or as we may choose to magnify or 

 to disregard slight differences. There are just as 

 many kinds of eels as there are races of men or of 

 dogs. Future naturalists will again describe those 

 eels ; but they will know them for what they are, — 

 the varying descendants of some one degenerated 

 type of fishes crawling in the weeds and ooze of 

 many seas and rivers, and thus variously modified 

 by their surroundings. 



The old notion of a species has passed away for- 

 ever. We can no more return to it than astronomers 

 can return to the Ptolemaic notion of the solar sys- 

 tem. The same lesson comes up from every hand. 

 It is the common experience of all students of 

 species in every field. We have learned it from 

 Gray and Engelmann and Coulter, and each of 

 the many students of American botany. We have 

 learned it from Baird and Allen and Coues and 

 Ridgway and Stejneger, and from all who have 

 made life studies of American birds. We have 

 learned it from Cope and Marsh and Leidy, and 

 from all who have rummaged in the tombs where 

 our ancestors lie buried. I do not know of a 

 naturalist in the world who has made a thoughtful 

 study of the relations of species in any group, who 

 entertains the old notion as to their distinct origin. 

 There is not one who could hold this view and 

 look an animal in the face. 



