AN INTERESTING POLYMORPHIC BUTTERFLY 1B8 
abundant enough for its presence to be of protective value 
to the mimic, any Pseudacrcea which is produced that does 
not conform very closely to the well-known distasteful model 
is more likely to be destroyed by enemies than a specimen 
which is almost indistinguishable from the model. 
On the island, however, the models are so extraordinarily 
scarce that an enemy of Pseudacrcea might quite conceivably 
never see one — hence their presence can have very little protec- 
tive value for the Pseudacrcea, so that a variety of Pseudacrcea 
would have as much chance of surviving as a specimen con- 
forming as closely as possible to the type of a model. If this 
explanation be the correct one the facts form a most convincing 
proof of the reality of mimicry, and of the power of natural 
selection to keep mimics up to the mark. 
The reason for the scarcity of models on the island is not 
certain — I believe it to be due to scarcity of food plant. The 
instances I have given do not nearly exhaust the complexity 
of this Pseudacrcea. In West Africa there are many forms, all 
believed by Dr. Jordan to be of this species. One, known as 
Ps. eurytus, gives the name to the whole of this polymorphic 
group, as it was the first one to be named by Linnseus. The 
male of this is reddish orange and black — the female black 
and white but of a pattern different from the black and white 
form already mentioned — the two sexes of this form copy 
accurately the two sexes of the model Planema epoea. In East 
Africa another dimorphic form exists, copying the dimorphic 
Planema aganice, form montana, this mimic, known as the form 
Rogersi, is known by a single specimen of each sex. 
In Natal occurs another form of this protean species of 
Pseudacrcea, known as imitator ; male and female are black and 
white, copying the corresponding sexes of the model ( Planema 
aganice) : the male is creamy where the female is white, so that, 
if we consider the various forms of Pseudacrcea eurytus, we 
find that in some localities the two sexes are alike, in others 
they are different, and in other places, as in Uganda, forms 
occur in which the two sexes are alike, mixed with other forms 
and with different sexes, and yet all of one species, breeding 
freely together. I have seen specimens of very different forms 
courting, and, as I have said, have bred one form from ova 
