1895.] Search for the Unknown Factors of Evolution. 425 
‘by experiment. Let phylogenic variation—a term first used 
‘by Nigeli"—include those departures from type which have 
become constant hereditary characters in certain phyletic 
‘series or even in a few generations. While all phylogenic 
variations must originate in ontogeny or in some stage of in- 
dividual development, certainly a very small proportion of the 
innumerable ontogenic variations which we find in the ex- 
amination or measurement of any adult individual ever be- 
come phylogenic, or constitute more than ripples upon the sur- 
face of a tide. 
This vital distinction has not been regarded hitherto. The 
statistics of variation, as compiled by Darwin and lately by 
Wallace, Weldon, Bateson, and others, do not take into ac- 
count that among phylogenic variations are others purely on- 
togenic springing up and disappearing during individual life, 
owing to causes connected solely with the disturbance of the 
typical action of the hereditary mechanism during ontogeny. 
In other words, these writers have without discrimination 
based upon variations, which may be largely or wholly onto- 
genic and temporary, the important principles of ‘ Fortuitous 
Variation’ of Darwin and of ‘Discontinuous Variation’ of 
Bateson, whereas it is only the laws of phylogenic variation 
which are of real bearing upon the problem of evolution. 
Take as an illustration of this false method the wing measure- 
ments of birds given by Wallace. Why may not these be 
largely cases of purely ontogenic variation due to influences of 
life habit or to some purely temporary disturbance of the 
hereditary basis? Above all others, the Neo-Darwinians must 
reconsider their principle of ‘fortuitous variation’ which is 
an induction from data of miscellaneous ontogenic and phyloge- 
nic variations, because Neo-Darwinism is essentially and ex- 
clusively a theory of the survival of favorable phylogenic 
variations. 
u Die Veränderung, die gewöhnlich der Vererbung gegenüber gestellt wird, steht 
nicht im Gegensatz zu dieser, sondern zur Constanz. In diesem Sinne heisst eine 
Veränderung constant, wenn das Gewonnene dauernd behalten, und vergänglich, 
wenn es bald wieder preisgegeben wird. Die constante oder die phylogenetische 
Veranderung . . . ist eigentlich nichts anderes als die rO ET des 
Idioplasmas. tPhkeohė der Abstammungslehre, p- 277. 
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