Seasonal Dimorphism in African Butterflies, 109 
A. lygus exist (which is not directly stated by Mr, 
Trimen) may link A. stenobea to typical A. lygus, and so 
to A. cecilia, but that they are a seasonal form of it in 
the extreme south seems exceedingly improbable ; they 
are far more likely to be a mere albinistic sport, such as 
occurs in many other species of Acrea. This seems the 
more probable from the fact that, as far as I have seen, 
they are always females. 
It is not at all a conclusive argument that, because in 
southern South Africa A. stenobea has not been found 
associated with A. caldarena and because, in Mashunaland, 
the latter occurs the whole year round without A. stenobea 
making its appearance, the two do not occur as seasonal 
forms of one species in any part of Africa. Nevertheless, 
as all the forms of A. cxcilia appear to occur chiefly iu 
Southern and South-Western Africa (although typical A. 
cecilia is also found in Abyssinia), I think the claim of 
A. caldarena to be regarded as distinct has a firm basis. 
Regarding this species as a wet-season form, we then still 
have to look for its dry development; and this leads me 
to point out to Mr. Marshall that, when he assumes that 
each species varies seasonally in the same way through- 
out its entire range, or, because it does not vary in cne 
district, it therefore varies nowhere, he makes an assump- 
tion which can be easily disproved by anybody in charge of 
a sufticiently large and carefully collected series of 
specimens.* 
When we see that A. zefes is the extreme wet develop- 
ment in Sierra Leone of that brightly coloured type of 
A. menippe found at Uganda, and that A. pseudegina is 
the extreme wet development in Sierra Leone of the 
southern A. natalica; whilst in both cases intermediate 
forms occur, sometimes side by side with the wet form, 
and sometimes, to the exclusion of both extremes, in inter- 
mediate localities, we must be very careful not to be too 
dogmatic in our statements respecting the constancy of 
either the species themselves, or their seasonal varieties. 
(5). A. pudorina, Staud. = A. cheribula, Oberth. 
Accepting Mr. Marshall’s correction as to the black- 
tipped forms being ‘‘wet” and the forms without 
black tips ‘dry,’ it is curious that in this species 
* By which I mean a series labelled, not only with exact 
localities, but with the dates of capture, and altitudes. 
