1894.] Neo-Lamarckism and Neo- Darwinism. 667 
transfer of these characters through the medium of the germ- 
plasm to “variations in its molecular constitution." In other 
words, there can be no heredity of a character which originates 
at the periphery of the individual, because there is no means 
of transferring its likeness to the germ. All modification of 
the offspring is predetermined in the germ-plasm ; and if the 
new organism becomes modified through contact with external 
agencies, such modification is lost with the death of the indi- 
vidual. “Characters only acquired by the operation of exter- 
nal circumstances acting during the life of the individual, 
cannot be transmitted.” “All the characters ee bites by the 
offspring are due to primary changes in the germ.” It is ad- 
mitted that the continued effect of impinging environment 
may, now and then, finally reach the germ-plasm, but not in 
the first generation in which such extraneous influence may 
be exercised. In other words, acquired characters cannot be 
hereditary. 
It would seem as if this hypothesis precluded the possibility 
of evolution or the continued modification of species, inasmuch 
as it does not accept the modifications arising directly from ex- 
ternal sources. But Weismann supposes that variation origi- 
nates—or at least all variation which is of permanent use to 
the species—from a union of the sexes, inasmuch as the unlike 
germ-plasms of two individuals unite; and from the variations 
thus induced are derived the materials upon which natural 
selection works in the struggle for existence. “I am entirely 
convinced," Weismann writes, “that the higher development 
of the organic world was only rendered possible by the intro- 
duction of sexual reproduction.” “Sexual reproduction has 
arisen by and for natural selection, as the only means by which 
the individual variations can be united and combined in every 
possible proportion.” 
It will be seen that Weismann is a Darwinian—a believer 
in natural selection as the one controlling process of evolution; 
but, unlike Darwin, he refers variation to sex and declares that 
any new or acquired character originating in the body of the - 
organism cannot be transmitted. The exact means or machi- —— 
nery oe which he supposes Eee to act, is rather RU 
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