506 JOURNAL, BOMBAY NATURAL HIST, SOCIETY, Vol. XXVIITF 
beticus) migrates in the Spring. In March at Rawalpindi I have observed this- 
species migrating for several weeks ; across a width ot 20 yards I counted 90 per 
minute passing during the period of greatest intensity ; throughout the whole 
period the direction was 5 degrees North of West. Again and again I have notic- 
ed butterflies flying in a definite direction ; they may turn aside to a flower or to- 
inspect a passer-by, but they eventually continue on in the same direction. In 
the Journal of the Entomological Society there have appeared recently some 
interesting articles dealing with the migrations of certain Pierids in the Island 
of Trinidad ; the butterflies apparently started at the South end of the island, 
travelied direct to the Northend, then turned West. leaving the island eventually 
in this direction for the mainland ot America. The density of these migrations 
were so great that motor cars had to stop moving on the roads, since nothing 
could be seen through the wind screens. 
{2. I should now like to touch lightly on the subject ot variation, regarding 
which much has been written, but there is no doubt that theory still predominates 
over proved facts. The whole subject is most fascinating and, as I said at the 
commencement of this article, not only do butterflies offer the best medium for 
its study but also that we ar2 better situated for the purpose in India than any- 
where else in the world. There are iour kinds of variation to be thought of ; 
sexual, individual, seasonal and geographical. Sexual variation can be dealt 
with very briefly. In many species the two sexes are almost indistinguishable ; 
in the majority there is a marked difference ; in a few there is no resemblance 
whatever between the sexes and it is only comparatively recently that they have’ 
been ascertained to belong to the same species. Among the nasty groups the re- 
semblance between th sexes is pretty close and this is also the case more or less 
amongst the group with cryptic undersides. In the unprotected groups there is 
usually a considerable difference ; it is the female that is always duller and less 
conspicuous than the male, while in certain genera the difterences between the- 
males of the various species is considerable, but the females are so alike as to 
require a first class expert to allocate them to their correct males. Ti isno doubt 
the object of Nature to preserve the life of the female for a longer period than the- 
male, since after fertilisation she has to devote her time to laying her eggs. 
Possibly Nature’s intention is that the bright coloured males in the unprotected 
groups should be sacrificed to the enemy, so that the insignificant females are 
preserved. 
13. Individual variation may arise from a number of causes ; different nutri- 
tion in the caterpillar stage, effect of light or temperature on the chrysalis, are 
probably the most important, but there are no doubt others that we do not even 
suspect at present. In some species the variation is extraordinary ; for instance’ 
the undersides of no two leaf butterflies are alike. Again in the little yellow 
Pierid (Terias) of the Indian garden the variation between individuals is tremend- 
ous. In many butterflies the variation is very small, but a minute examination 
will show that no two individuals are exactly alike any more than are two human 
beings. All the varieties of this class can be more or less linked together by 
intergradations, provided one can obtain a long enough series. There is, how- 
ever, another class or individual variation, where very distinct varieties occur’ 
that cannot be linked together ; this kind of variation is called dimorphism. 
For instance a few species of Papilionids exist in two totally different forms in 
both sexes. Two other Papilionids each have three totally different forms of 
females. In one of these, the black-bodied Papilio polytes, the first form of 
female resembles the male and is comparatively rare ; the second resembles a 
rusty red-bodied swallowtail, which only occurs in the peninsular portion of 
India, where alone this form of female is to be found though the species is met 
with nearly everywhere ; the third and commonest form is like another red 
bodied swallowtail found everywhere. There is yet another kind of individual 
Variation known as an aberration or sport ; these are rare but occur in some 
