LEPIDOPTERA. 409 



that resemble the ill-smelling ones, even though they do not 

 possess a similar odor. According to the theory of natural 

 selection these resemblances have been produced as follows. 

 In the case of a variable species that is unprotected by any 

 disagreeable quality, any variation towards a protected spe- 

 cies will tend to preserve the life of the individual possessing 

 it. And in turn such offspring of these individuals as still 

 more nearly resemble the protected species will be most 

 likely to be preserved. The continued action of this natural 

 selection will result in producing a species that closely re- 

 sembles the protected one, even though it may be very 

 different structurally from the one that it mimics. 



Many instances of unconscious mimicry of this kind are 

 known. They are especially abundant in the tropics where 

 the foul-smelling Heliconince are most abundant. The bad 

 odor of these butterflies when living is so marked that it 

 can be detected by the human nose ; and it is found that 

 many species of them are mimicked by other butterflies, and 

 especially those of the Pieridae. The mimicry is not con- 

 fined to similarity in coloring, but extends to the shape of 

 the wings and manner of flight. 



The larva of the Viceroy feeds upon willow, poplar, balm 

 of gilead, aspen, and cottonwood. The species two- or three- 

 brooded, and hibernates as a partially grown larva in a 

 nest made of a rolled leaf. This nest is lined with silk, 

 and the leaf is fastened to the twig with silk so that it can- 

 not fall during the winter. Mr. Scudder states that so far 

 as is known to him all of the species of the Sovereigns hi- 

 bernate as larvae in nests of this kind. It is worthy of note 

 that only the autumn brood of caterpillars make these nests. 

 So that the nest-building instinct appears only in alternate 

 generations, or even less frequently when the species is 

 more than two-brooded. B. archippus is found over nearly 

 the whole of the United States as far west as the Sierra 

 Nevada Mountains, and has been found sparingly even to 

 the Pacific coast near our northern boundaries. 



