1894. | NEW YORK ACADEMY OF SCIENCES. 157 
cases too complex to be interpreted as the effects solely of use 
and disease. The ventricle by eombined use grows no thicker 
than requisite, because it selects the thickness best suited to 
survive. Use and disuse should have affected external struc- 
tures best, yet the skin retains tenaciously its ancestral charac- 
ters; the oldest birds were feathered, the oldest mammals pos- 
sessed hair. 
The direct action of cold, serving in higher animals as a heat 
stimulus, is interpretable alone as a result of selection. 
Instinet, if the hereditary memory of experience, can only 
maintain in the higher animals. In the lower animals to avoid 
experience is the only chance of survival. Mimicry is alone ex- 
plained by selection, for it is always the rarer form that assumes 
the characters of distasteful or otherwise protected forms. 
Prof. Cope, replying to the discussion of Prof. Poulton, main- 
tained that selection did not explain the origin of variations. 
It required conditions which could not be obtained; for its 
purpose there must fortuitously be found two varying indi- 
dividuals of either sex, whose progeny, if at all varying, would 
have to maintain themselves against the entire species. Use 
and disuse (or movement and lack of movement) is the directive 
power towards variation, pressing its physical necessity upon 
the plastic animal form, not merely in one individual but ina 
race. As in the reduction of digits in horses, the effect was not 
transitory but constant—for all individuals and at all times. 
Physiogenesis expresses the immediate influence of environ- 
ment, stimulated by direct physical causes. Kinetogenesis by 
the animals’ movements gives rise to organic changes. Joint 
formation is directly kinetogenetic, as the formation of new 
joints after dislocations tends to demonstrate. External stim- 
uli should affect simultaneously both the body and the germ 
plasm. Selection can but operate with existing structures, but 
the origin of these is to be explained by direct needs of environ- 
ment. In the case of the lower animals’ inability to acquire per- 
sonal experience, was it not possible that this might be acquired 
by the observation of the experience of others? 
Prof. E. B. Wilson noted briefly the lack of evidence on the 
