ILLUSTRATIVE OF NATURAL SELECTION. 185 
upon leaves, render it especially advantageous for 
‘them to have some additional protection. This they 
at once obtain by acquiring 1 resemblance to other 
species which, from whatever cause, enjoy a compara- 
tive immunity from persecution. 
Concluding remarks on Variation in Lepidoptera. 
This summary of the more interesting phenomena 
of variation presented by the eastern Papilionide is, 
I think, sufficient to substantiate my position, that 
the Lepidoptera are a group that offer especial faci- 
lities for such inquiries; and it will also show that 
they have undergone an amount of special adaptive 
modification rarely equalled among the more highly 
organized animals. And, among the Lepidoptera, the 
great and pre-eminently tropical families of Papilionide 
and Danaide seem to be those in which complicated 
adaptations to the surrounding organic and inorganic 
universe ‘have been most completely developed, offer- 
ing in this respect a striking analogy to the equally 
extraordinary, though totally different, adaptations 
which present themselves in the Orchidex, the only 
family of plants in which mimicry of other organisms 
appears to play any important part, and the only one 
in which cases of conspicuous polymorphism occur ; for 
as such we must class the male, female, and hermaph- 
rodite forms of Catasetum tridentatum, which differ so 
greatly in form and structure that they were long con- 
sidered to belong to three distinct genera. 
