1034 The American Naturalist. [November, 
latter exhibit slight sexual dissimilarity, that their colors are ob- 
scure, and therefore the theory that distinctive secondary charac- 
ters and strongly-marked sexual differences are necessary ad- 
juncts to polygamous habit is disproved. This conclusion ap- 
pears reasonable; but if we examine the sexes of both species 
during courtship the contrast between their respective males and 
females is very great, and the exhibition of secondary characters 
evident. In both the males possess large cervical appendages, 
which, during the reproductive period, assume a dark orange hue 
and are capable of voluntary inflation. In Centrocercus this disten- 
sion is enormous, and observers who have witnessed the males at 
their leks assert that their natural appearance is thereby changed 
beyond recognition. In Cupidonia this inflation is further supple- 
mented by overlying wing-like tufts, which, in connection with 
the crown and tail feathers, are erected on occasions of parade. 
Any one who will take the trouble and patience to observe these 
birds during the pairing season will not fail to wonder at the 
transformation of the cocks, and freely admit the possession by 
them alone of strongly characteristic sexual features. Worthy 
of remark, on the other hand, is. the lack of these sexual differ- 
ences in other nearly allied plain-haunting species, as exhibited 
by the monogamous red grouse and ptarmigan (Tetrao scoticus 
and Lagopus albus). 
In the case of plain-loving species the results of sexual selection 
have been counteracted by the law of survival. So soon as any 
males became, in consequence of sexual selection, more conspic- 
uous than the rest, they would be the most likely victims to 
beasts of prey by virtue of that superiority, while the less attrac- 
tive would survive; and so the tendency toward high ornamenta- 
tion would be thwarted as long as the species continued to exist 
under unaltered conditions of environment. The necessity of 
protective resemblance to many birds has thus exerted a control- 
ling influence on sexual selection, and indirectly on polygamy 
itself. 
The ability of organism to evade (so to speak) the laws of 
nature, or rather to compromise with conflicting laws, is curiously 
exhibited in the pinnate grouse. In it the selective tendency, in 
