264 BIOLOGICAL LECTURES. 



erated in a succeeding one. Thus, in the reduction of digits 

 the hindfoot is more rapidly modernized than the forefoot. 

 In Protylopus, for example, the hand has still four functional 

 digits, while the pes already has but two ; in the succeeding 

 Poebrotherium both manus and pes are in the same stage of 

 simplification, with two functional digits, and two small nodules 

 representing the rudiments of the lateral pair. But while one 

 structure may thus be retarded in its development and another 

 accelerated, the differentiation of the organism, as a whole, 

 keeps steadily advancing. It almost seems as if the animals 

 were consciously striving for a goal, though, of course, this is 

 only an impression given by the direct and unswerving course 

 their evolution takes. 



There are many other " morals " which might be drawn from 

 the history of the American selenodonts, but I shall lay no 

 further tax upon your patience. If it seems to you that I am 

 attributing too much importance to palaeontology and ignoring 

 other means of investigation, this is simply because to praise 

 morphology and physiology in Wood's Holl w6uld be carrying 

 coals to Newcastle. The fair structure of our science must be 

 reared upon a broad and deep foundation, not of a single 

 department of inquiry, but of all of them combined and " fitly 

 joined together." 



