THE STUDY OF STRUCTURE. 347 



student of the wholly extinct Graptolites has no clue 

 such as he has who studies fossil corals. Yet the 

 study of these lost races is of profound interest, since 

 they must be fitted into their appropriate place in 

 the general scheme of zoological or botanical classi- 

 fication. 



The famous French palaeontologist, Albert Gaudry, 

 has spoken thus of the extinction of races : " A host 

 of creatures have vanished; the most powerful, the 

 most fertile have not been spared. There is a sad- 

 ness in the spectacle of so many inexplicable losses." 

 Let us linger for a little over the fact the details 

 of which have been accumulated with consummate 

 patience through the past century. 



It seems clear from the rock-record that sudden 

 disappearance has been very rare. The American 

 bison's practical extermination in a few years is 

 without parallel in pre-human days. Races waned 

 and died out, but were not suddenly extinguished. 

 They did not come to a catastrophic end. Another 

 striking fact is that while evidences of senility have 

 been detected in some of the last representatives of 

 dwindling races, there are many cases where a full 

 stop seems to have been put to the history of a stock 

 while it was still in its prime. "Nor is there any 

 reason to speak of an elimination of weaklings; as 

 Gaudry says : " While insignificant creatures per- 

 sist, the princes of the animal world vanish with- 

 out return." 



The problem of the causes which led to the extinc- 

 tion of races has been left by the nineteenth century 

 unsolved. It is easy enough to refer to changes of 

 environment for which the plasticity of the organism 

 was insufficient, or to the struggle for existence be- 

 tween cuttlefishes and trilobites, between ichthyo- 



