398 SCOTT. [Vol. V. 



latter theory attempting no explanation of the causes of varia- 

 tion. Nor is it for a moment pretended that use and disuse are 

 the sole or even the chief factors in variation. On the contrary, 

 we know that many other and even more important factors 

 enter into the process. 



Turning now to Professor Morgan's criticisms of the palaeon- 

 tological evidence, we may say that the objection drawn from the 

 imperfection of the geological record and from the small num- 

 ber of individuals contained in the museums, can be allowed 

 little weight. So far as several of the mammalian phyla are 

 concerned, the number of missing links must be very small, the 

 wonderful series of American fresh-water Tertiaries being in 

 this respect quite unrivalled in the known world. Of the bet- 

 ter known species, the collections already contain hundreds 

 and sometimes thousands of individuals available for study. If 

 results obtained from such material point in one direction, it is 

 surely most illogical to assume that specimens yet to be dis- 

 covered will probably lead to opposite conclusions. The prob- 

 abilities are all the other way. Professor Morgan seems also 

 to suppose that individuals "in the early stages of life " are 

 uncommon as fossils ; but this is very far from being the case ; 

 they are abundantly represented in the collections and show no 

 more tendency to indeterminate variation than do the adults. 

 But even were the young stages unknown, before their absence 

 could be allowed weight as an objection, it would be necessary 

 to show that such very slight changes were of "elimination 

 value." 



I am unable to see why the evidence afforded by foot-struc- 

 ture is any less cogent in support of determinate variations than 

 that derived from the teeth, except in so far that not nearly so 

 many completely preserved feet are found. But where they do 

 occur in numbers, the result is the same. The carpus and 

 tarsus of the equine series from HyracotJierium to Equus form 

 as striking an example of this as could be desired. The non- 

 mechanical variations do not occur. The difficulty of compre- 

 hending how teeth can be modified by use, must be freely 

 admitted. But it should be remembered that a completely 

 formed tooth is not by any means a dead, inorganic mass. Its 

 health depends upon use, and I have seen fossils which clearly 

 demonstrate the ill-effects of disuse of teeth in the individual. 



