Summary and General Conclusions 459 
appears, and is inherited in its new form. From the re- 
sults of De Vries it appears that mutations are sometimes 
scattering, at least in the case of the evening primrose. 
From such scattering mutations, the smaller species or 
varieties (in so far as these do not depend on local con- 
ditions) arise. There is here an important point of agree- 
ment with Darwin’s idea in regard to evolution, inasmuch as 
he supposed that varieties are incipient species. Our point 
of view is different, however, in that we do not suppose these 
varieties (mutations) to have been gradually formed out of 
fluctuating variations by a process of selection, but to have 
arisen at once by a single mutation. It also appears that in 
some cases a single new mutation may develop in a species. 
We may suppose that the new form might in such a case 
supplant the parent species by absorbing it, or both may go 
on living side by side, as will be more likely the case if they 
are adapted to somewhat different conditions. 
A number of writers have supposed that evolution marches 
steadily forward toward its final goal, which may even 
lead in some cases to the final but inevitable destruction 
of the species. By certain writers this view has been called 
orthogenesis, although at other times the idea is not so much 
that there is advance in a straight line, as advance in all 
directions. This appears to be Nageli’s view. It gives a 
splendid picture of the organic world, as irresistibly marching 
toward its goal, —a relentless process in some cases, leading 
to final annihilation, a beneficent process in other cases, 
leading to the fullest perfection of form of which the type is 
capable. Compared with the vacillating progress which is 
supposed to be the outcome of individual selection, this view 
of progression has a grandeur that appeals directly to the imag- 
ination. We must be guided, however, by evidence, rather 
than by sentiment. The case will, moreover, bear closer 
scrutiny. If evolution has indeed taken place by the survi- 
val of a series of mutations, whose origin has no connection 
