132 AN INTERESTING POLYMORPHIC BUTTERFLY 
the sexes were similar also in Ps. obscura, resembling the 
fourth type. 
These several models and mimics have been made known 
largely through the collections made by Dr. Wiggins at Entebbe, 
in the forests near to which all these forms may be taken flying 
together. The various models of genus Planema are un- 
doubtedly of different species. Some time ago, however, 
Dr. Karl Jordan of Tring suggested that all the forms of 
Pseudacroea mentioned were of one species, basing his hypo- 
thesis on the anatomy of the male armature. When I went 
out to Bugalla Island in 1912 I soon found that all these forms 
of Pseudacroea were very abundant, but extraordinarily 
variable, so that specimens intermediate between any of the 
other types were as common as the type ; this very strong 
evidence in favour of Dr. Jordan’s hypothesis was confirmed 
in August 1912, when I was able to breed, from ova deposited 
by one form, types of other forms, and intermediate specimens 
so that the four forms of Pseudacroea mentioned are all of one 
species, accurately resembling different species of Planema , 
some of which have the sexes similar, some dissimilar. I may 
say that the resemblance of model to mimic is extraordinarily 
close, and for a long time I was deceived over and over again. 
The Pseudacroea, is however, very much more wary than the 
model and never rests with the complete ‘ abandon ’ exhibited 
by the Planema. One learns to recognise them apart by 
degrees, mainly through the different habit of flight. 
The particularly interesting feature about the island 
Pseudacroea was the extraordinary degree of variability. The 
large collections of the same species made by Dr. Wiggins 
on the mainland at Entebbe, only some twenty-five miles 
north-east, show that the mimics there keep very true to 
the types of their models and specimens intermediate between 
two types are excessively uncommon. The great variability 
of the Pseudacroea on the island was correlated with great 
scarcity of models. Indeed during the fourteen months 
on Bugalla, of one model ( Planema poggei) I only caught two 
males. The mimics many times outnumbered the models. 
I believe this fact supplies the reason for the great variability 
of the mimics. On the mainland, where the model Planema is 
