cumulated, the more they seemed to him to strengthen the 
conclusion that the altered temperature-conditions were 
capable of acting as a stimulus to which each organism would 
respond according to its own pre-arranged constitution, and 
that it was only in comparatively rare cases that the new 
conditions operated as the causa efficiens of the change. (See 
Weismann’s Romanes’ Lecture, 1894.) Even in such an 
instance as that of P. phleas, it was, perhaps, too much to 
assume that the darkening of the scales was the direct result 
of a high temperature, for in other cases the same temperature- 
conditions led to the opposite result. If we pushed the matter 
further and proceeded to ask what was the nature of the 
pre-arrangement of material which enabled different species, 
during growth, to respond in a different manner to the same 
stimulus, and in many cases to respond by reverting to an 
earlier phylogenetic stage, we found ourselves at once on 
very debatable ground. It might, however, safely be borne in 
mind that under either of the two leading theories of heredity 
—the centripetal and centrifugal—it was perfectly con- 
ceivable that a competition took place during the growth of 
every organism between various elementary constituents— 
call them what we please—the greater number of which were 
destined to take no part in the somatic structure of the adult 
organism, though they might still be transmitted in a latent 
condition, through the germinal material, to succeeding 
generations. To the revival into efficient activity, under 
exceptional conditions, of some of these usually latent 
‘determinants ’”’ or ‘‘ gemmules,’’ he was inclined to attribute 
such remarkable instances of atavism as those now exhibited 
by Mr. Merrifield. 
Mr. Barrett said he was interested to find that one of the 
forced forms of L. sibylla was similar to a specimen he had 
seen which had emerged from the pupa during a thunder- 
storm. 
Mr. F. W. Frohawk, in connection with Mr. Merrifield’s 
paper, exhibited a series of 200 specimens of V. C-albwn 
bred from one female taken in Herefordshire, in April, 1894. 
The series consisted of 105 males and 95 females, and 
included 41 specimens of the hght form, and 159 of the 
dark form. 
