( ix) 
Pseudacrxa serving as a link between the immense Papi/io and 
the comparatively small but dominant and central Acreine 
members. The inclusion of antimachus, in spite of its size, in 
this powerful combination seemed more satisfactory than Mr. 
Trimen’s supposition in 1868 that it “is possibly an instance 
of special modification in imitation of some gigantic Acrea as 
yet unknown, or perhaps extinct” (Trans. Linn. Soc., vol. 
xxvi, 1870, p. 503). Professor Poutton suggested that it was 
possible that the remarkable bluish-grey patches on the under- 
side of the fore-wing of antimachus were traces of descent from 
an ancestor common to it and the other equally extraordinary 
and equally isolated species of the genus Drurya,—D, zalmoxis. 
In the discussion which followed the exhibit Professor 
Poutton suggested that the struggle for existence against the 
attacks of young, inexperienced enemies,—the kind of selective 
attack to which ex hypothesi Miillerian (synaposematic) resem- 
blance was due—was in reality far more severe than appeared 
at first sight because of the pressure of the struggle upon the 
enemies themselves. This pressure was chiefly felt by the young, 
and it was so excessive that comparatively few individuals in 
the fresh wave sent forth at each breeding season, survived 
to become mature and experienced. It followed from this fact 
that the amount of selective pressure exerted by inexperienced 
enemies of insects was ten, twenty, a hundred, at any rate 
many times as great as that which was due to the educational 
period of the mature enemies existing at any moment. 
With reference to the PresipENt’s remarks, on the great 
size of Drurya antimachus compared to that of the other 
members of the synaposematic group, Mr, F. A. Heron sug- 
gested that, in the recognition of prey by sight, size,—within 
considerable limits,—might be of minor importance to color- 
ation,—-the term being used to cover every kind of pattern 
and marking. The size of an insect, as correlated with the 
idea of its distance, was, in natural surroundings, under 
varying atmospheric conditions, extremely difficult of exact 
estimation, though it might be easily observable in a group 
of other insects of known size in a standard cabinet drawer. 
Distance, and its correlative size, might perhaps be especi- 
ally hard of determination by animals which, like the 
