anew in response to stimulation, only the power of acquiring it being transmissible. As regards this power also, just as regards instinct, there is not a vestige of proof that it is increased by stimulation, by use. On the contrary, it is a matter of common knowledge, that as animals grow older their long stimulated powers of acquiring mental traits become more feeble and tend to cease. The conclusion we are forced to arrive at, then, is this—that since whatever mental that is transmissible (instincts and powers of acquiring reason) does not vary under stimulation, therefore no acquired mental traits can be transmitted, for no transmissible mental traits can be acquired—an à priori conclusion capable, as will be seen, of ample à posteriori confirmation.
It may be objected that, since reflexes and instincts appeared earlier in the phylogeny than reason, they ought to appear earlier in the ontogeny, whereas some reflexes and instincts, e.g. those pertaining in man to the sexual functions, appear later in the ontogeny than reason. The answer to this is threefold: (1) some reflexes and instincts which appear late in the ontogeny, without doubt have had the period of their appearance in it shifted by the action of Natural Selection—have been removed to a later date by the accumulation of favourable variations; (2) others again may exist in a latent state from an early period, not becoming apparent till stimulation is supplied, which stimulation is not supplied till late in the ontogeny; (3) others again may not have been developed till late in the phylogeny, just as some structures (e.g. horns and teeth), which do not vary under stimulation, were not developed till late in the phylogeny.
In defining instinct as "the faculty which is concerned in the conscious adaption of means to ends by virtue of inborn inherited knowledge and ways of
