14 Darwin, and after Darwin. 



both sets of causes are supposed to be in operation 

 together, we have no means of estimating the relative 

 shares which they have had in bringing about these 

 results. Of course there are large numbers of cases 

 where it cannot possibly be supposed that the 

 Lamarckian factors have taken any part at all in pro- 

 ducing the observed effects ; and therefore in such cases 

 there is almost full agreement among evolutionists in 

 theoretically ascribing such effects to the exclusive 

 agency of natural selection. Of such, for instance, are 

 the facts of protective colouring, of mimicry, of the 

 growth of parts which, although useful, are never 

 active (e.g. shells of mollusks, hard coverings of seeds), 

 and so on. But in the majority of cases where 

 adaptive structures are concerned, there is no means 

 of discriminating between the influences of the 

 Lamarckian and the Darwinian factors. Conse- 

 quently, if by the Neo-Lamarckian school we under- 

 stand all those naturalists who assign any higher 

 importance to the Lamarckian factors than was 

 assigned to them by Darwin, we may observe that 

 members of this school differ very greatly among 

 themselves as to the degree of importance that ought 

 to be assigned. On the one hand we have, in Europe, 

 Giard, Perrier, and Eimer, who stand nearer to Dar- 

 win than do a number of the American representatives 

 — of whom the most prominent are Cope, Osborn, 

 Packard, Hyatt, Brooks, Ryder, and Dall. The most 

 extreme of these is Professor Cope, whose collection 

 of essays entitled The Origin of the Fittest, as well as 

 his more recent and elaborate monograph on The 

 Development of the Hard Parts of the Mammalia, 

 represent what appears even to some other members 



