Notes on Seasonal Dimorphism. 
427 
defined upon a generally duller greenish, ground. Eronia 
leda is no exception to the same rules for winter forms. 
The dry season brood show a narrower border to apices 
of forewings, and are generally smaller in size than the 
summer brood. The orange of the underside is deeper 
in colour, and the flecking of the hindwings denser. 
I have noticed no marked seasonal difi'erentiation 
among the Papilioninse. P. demoleus, which appears 
more or less throughout the year, shows generally rather 
smaller during the dry season months, but I know of no 
other variation. 
This brings me to the end of my theme, as I have not 
sufficient data to do justice to such seasonal changes as 
may occur amongst the obscure family of the Hes'peridse. 
My only ambition has been to lead Lepidopterists to 
turn more of their attention to the very marked seasonal 
differentiation which, nearly all butterflies exhibit that 
fly throughout the year. The collective testimony of a 
large number of Natal butterflies differentiating season- 
ally, on certain well-deflned principles, ought to bear due 
weight in the determining of doubtful species. This 
identification of species can best be aided by paying the 
utmost attention to dates of capture, with due regard to 
the character and climate of the country the butterfly may 
come from. 
As regards the Fierinse, any butterflies showing a 
strongly-tinted underside, with or without freckling, I 
should feel inclined to attribute to a dry season, or modi- 
fied form of some wet season congener yet to be identified. 
There may, doubtless, be exceptions to this ruling, 
especially as regards butterflies living in dry, arid countries, 
where the conditions of existence are no more favourable 
to perfect development than the winters of more luxuriant 
countries. 
In conclusion, I can only add that the present system 
of adding species to species, on the mere ground of some 
slight modification of the markings of the upper or under- 
side, and sometimes on the strength of one or two 
examples, is most misleading. Even as regards such 
slight structural differences as the lesser or greater com- 
parative length of the radial nervules, one to the other, 
due weight should be given to the tendency of dry season 
forms to adopt acuter forewings, which must manifestly 
aff'ect the relative proportions of these nervules. 
