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tures, its rivers, lakes, peaks and cliffs. The detail must be worked out 
by those who come after. In the case of Darwin the map remains sub- 
stantially as it was, although many have worked at the various details 
with which the modern chart is filling up. The discovery of the micro- 
scope has enabled us to frame a rational theory of heredity and to under- 
stand with some degree of certainty the physical basis of the functions 
of inheritance. The morphology of animals has been very fruitfully studied 
by many men. Many others have developed the history of past life on the 
earth, and we would have to have a theory of evolution to account for 
this, if Darwin had not furnished one already. 
The three men most famous since Darwin are these: Wagner, Weiss- 
mann and Mendel. Mendel died before Darwin wrote and his work on the 
“Heredity of Peas’ was forgotten until after Darwin’s time, but has be- 
come a very important factor in our experimental studies of living forms 
in relation to inheritance. Wagner was the first one to lay adequate stress 
on the idea of isolation as a species-forming influence. His weakness was 
that he rejected selection as an element, assigning to isolation the impos- 
sible task of accounting for all the external phenomena in the origin of 
species. To Weismann we owe more than to any one else our present 
knowledge of heredity. 
Theories of less importance are Eimer’s orthogenesis, which has a 
good deal behind it, and which we shall probably accept if some genius 
will arise to tell us what it means. It rests on the fact that we have many 
long series of animals which seem to have progressively varied as time 
went on. 
The study of the mutations of the evening primrose by De Vries has 
given many hints as to possibilities in plant breeding. I do not believe that 
the theory that species are mainly or largely formed by sudden mutations 
will survive the present generation of De Vries’ followers, but the impulse 
given to experimental study of plants will long continue. 
More than thirty years ago I used these words in Indianapolis: 
“Darwin lies in Westminster Abbey, by the side of Isaac Newton, one 
of the noble men of the past whose life had made his own life possible. 
Of all who have written or spoken, by none has an unkind word been said. 
His was a gentle, patient and reverent spirit, and by his death has not 
only science, but our conception of Christ, been advanced and ennobled.” 
