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 a 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 Papilionidse 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 Papilionida3 

 and Danaida3 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 Orchidea?, 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. 



