Views of Thomson and Geddes 
male organisms are the result of this male ten- 
dency to dissipate energy. In the spermatozoon 
the dissipated energy appears in the form of 
active movement ; in the adult organism it takes 
the shape of plumes and other ornaments, of song 
and contests for the females. 
This theory, however, does not explain what 
we might call the haphazard nature of sexual 
dimorphism. If sexual dissimilarity is due to the 
tendency of the male to dissipate energy, why do 
we see very marked dimorphism in one species, 
and no dimorphism in a very nearly allied 
species? Why are the males larger than the 
females in some species, and smaller in other 
species? Again, how is it that in certain species 
of birds—the quails of the genus Zuruzx, the 
Painted Snipe (Rhynchea), and the Phalaropes— 
it is the female who possesses the more showy 
‘plumage? Moreover, this theory, equally with 
that of Wallace, does not explain why the ex- 
crescences which characterise the male appear in 
various parts of the body in different species. 
STOLZMANN’S THEORY 
Stolzmann has made an ingenious attempt to 
explain why in birds the cock is so frequently 
more conspicuously coloured than the hen. He 
asserts that among birds the males are more 
numerous than the females, and that this pre- 
ponderance is not advantageous to the species. 
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