IV.] MINUTE MODIFICATIONS. 123 



The amphibia {i.e. frogs, toads, and efts) were long con- 

 sidered (and are so still by some) to be reptiles, showing 

 an affinity to fishes. It now appears that they form with 

 the latter one great group — the ichthyopsida of Pro- 

 fessor Huxley — which differs widely from reptiles ; while 

 its two component classes (fishes and amphibians) are 

 difficult to separate from each other in a thoroughly 

 satisfactory manner. 



If we admit the hypothesis of gradual and minute modi- 

 fication, the succession of organisms on this planet must 

 have been a progress from the more general to the more 

 special, and no doubt this has been the case in the majority 

 of instances. Yet it cannot be denied that some of the 

 most recently formed fossils show a structure singularly 

 more generalized than any exhibited by older allied forms ; 

 while others are more specialized than are any similar 

 creatures of the existing creation. 



A notable example of the former circumstance is offered 

 by macrauchenia, a hoofed animal, which was at first 

 supposed to be a kind of great llama (whence its name) — 

 the llama being a ruminant, which, like all the rest, has 

 two toes to each foot. Now hoofed animals are divisible 

 into two very distinct series, according as the number of 

 functional toes on each hind foot is odd or even. And 

 many other characters are found to" go with this obvious 

 one. Even the very earliest Ungulata show this distinc- 

 tion, which is completely developed and marked even in 

 the Eocene pala*otherium and anoplotherium found in 

 Paris by Cuvier. The former of these has the toes odd 

 (perissodactyle), the other has them even (artiodactyle). 



Now, the macrauchenia, from the first relics of it which 

 were found, was thought to belong, as has been said, to 



