THE EXTINCT MAMMALIA. 299 



another one has become diversified in a different period ; and so 

 each one has its history, some beginning farther back than others, 

 some reaching far back beyond the very beginning of the time 

 when fossils could be preserved. I call attention to this view be- 

 cause it is a very easy matter for us to use words for the purpose 

 of confusing the mind ; for, next to the power of language to ex- 

 press clear ideas, is its power of expressing no ideas at all. As we 

 all know, we can say many things which we can not tliink. It is 

 a very easy thing to say twice two are equal to six, but it is im- 

 possible to think it. 



I would cite what I mean by variations of species in one of its 

 phases : I mention a genus of snakes, Ophibolus, which is found 

 in the United States. If we take the species of this snake-genus 

 as found in the Northern States, we have a good many species well 

 defined. If we go to the Gulf States, and examine our material, 

 we see we have certain other species well defined, and they are 

 very nicely distinguished. If, now, we go to the Pacific coast, to 

 Arizona and New Mexico, we shall find another set of species 

 well defined indeed. If we take all these different types of our 

 specimens of different localities together, our species, as the Ger- 

 mans say, all tumble together : definitions disappear, and we have 

 to recognize, out of the preliminary list of thirteen or fourteen, 

 only four or five. That is simply a case of the kind of fact with 

 which every biologist is perfectly familiar. 



When we come to the history of the extinct forms of life, it is 

 perfectly true that we can not observe the process of descent in 

 actual operation, because, forsooth, fossils are necessarily dead. 

 We can not perceive any activities, because fossils have ceased to 

 act. But, if this doctrine be true, we should get the series, if 

 there be such a thing ; and we do, as a matter of fact, find longer 

 or shorter series of structures, series of organisms proceeding from 

 one form into another form, which are exactly as they ought to 

 be if this process of development by descent had taken place. 



I am careful to say this ; because it is literally true, as we all 

 must admit, that species must fall into some kind of order or 

 other. You could not collect bottles, you could not collect old 

 shoes, but you could make some kind of a serial order of them. 

 There are, no doubt, characters by which such and such shoes 

 could be distinguished from other shoes, these bottles from other 

 bottles. But if serial order does not prove evolution, as is too 

 often assumed, we have in recent forms of life in zoology and 



