
1890.] Embryology. 87 
we can appeal, without interjecting gemmules, plastidules, pangens or 
some other accessory and needless agency into living organisms, as the 
efficient agents in the transmission of hereditary traits, we are restrict- 
ed in our choice to metabolism alone. In this way only is it possible 
to get rid of a deus ex machina in the form of an idioplasm in the 
sense first implied by Nageli, or of the gemmules of Darwin and 
Brooks, the plastidules of Haeckel, the pangens of De Vries, or the 
physiological units of H. Spencer. 
The preceding paragraph contains, in essence, my own hypothesis 
according to which all the facts of hereditary transmission and varia- 
tion may be codrdinated without losing or rendering unavailable the 
advantages which may be derived from the supposition that acquired 
characters may be transmitted. 
On my view metabolism itself becomes the means of transmitting 
the changes in the adult organism, due to the complex interaction 
between it and its surroundings to the idle, functionless and passive 
germ-cells, because it is a demonstrable fact that these are the only 
cells in a multicellular organism which have no work to perform which 
is of direct benefit to the individual life of that organism, unless it 
may be to take up the surplus nutriment not used up by the metabol- 
ism of the parent-body in the secular exhibition of the sum total of 
its physiological energies, in the struggle for existence. 
On my view the idioplasmic or specific molecular character of the plasma 
of the germ-cells, in common with that of the protoplasm of the whole body 
(which latter always tends to repair injuries, or even, in lower forms, 
replace lost parts), tends, in virtue of its acquired specific traits, to repeat 
the organization of its parent type, in the course of its development, not 
because it is something different from the protoplasm of the cells of the 
rest of the body, but because it ts wholly unspecialized and without physi- 
ological differentiation, as first urged by Prof. Huxley and subsequently 
maintained by H. Spencer. Molecular impressions experienced in 
the course of variations in the modes of manifestation of or disturb- 
ances of the balance of the metabolism of the parent-body are sup- 
` posed upon this view to be transmitted as molecular tendencies to the 
idle or passive plasma of the germ-cells. Variations in the molecular 
constitution and tendencies of the germinal matter are supposed to 
thus arise at different times in the same parent, and that, consequently, 
successive germs may be thus differently impressed. In this way also 
the molecular tendencies of the plasma of the germ-cells of different 
individuals may be also modified simultaneously or successively 
through the effect of enforced changes in the metabolism of multitudes 
