282 THE PRINCIPLES OF [Part II. 



extreme cases of close sexual resemblance and wide dis- 

 similarity, as those of the Crossoptilon and peacock, many 

 intermediate ones could be given, in which the characters 

 follow in their order of development our two rules. 



As most insects emerge from their pupal state in a 

 mature condition, it is doubtful whether the period of de- 

 velopment determines the transference of their characters 

 to one or both sexes. But we do not know that the col- 

 ored scales, for instance, in two species of butterflies, in 

 one of which the sexes differ in color, while in the other 

 they are alike, are developed at the same relative age in 

 the cocoon. Nor do we know whether all the scales are 

 simultaneously developed on the wings of the same spe- 

 cies of butterfly, in which certain colored marks are con- 

 fined to one sex, while other marks are common to both 

 sexes. A difference of this kind in the period of develop- 

 ment is not so improbable as it may at first appear ; for, 

 with the Orthoptera, which assume their adult state, not 

 by a single metamorphosis, but by a succession of moults, 

 the young males of some species at first resemble the fe- 

 males, and acquire their distinctive masculine characters 

 only during a later moult. Strictly analogous cases occur 

 during the successive moults of certain male crustaceans. 



We have as ^yet only considered the transference of 

 characters, relatively to their period of development, with 

 species in a natural state ; we will now turn to domesti- 

 cated animals; first touching on monstrosities and dis- 

 eases. The presence of supernumerary digits, and the 



mage, and to a considerable degree in the speculum, which is pure white 

 in the male and grayish-white in the female. Now the young males at 

 ri^st resemble, in all respects, the female, and have a grayish-white spec- 

 \iiim, but this becomes pure white at an earlier age than that at which 

 the adult male acquires his other more strongly-marked sexual differ- 

 ences in plumage : see Audubon, ' Ornithological Biography,' vol. iii 

 1835, pp. 249, 250 



