The Descent of Man

nished with peculiar thread-like bodies, which
are believed to act as smelling-organs, and these
are much more numerous in the males than
in the females. As the males, without any unusual
development of their olfactory organs,
would almost certainly be able sooner or later
to find the females, the increased number of the
smelling-threads has probably been acquired
through sexual selection, by the better provided
males having been the more successful in finding
partners and in producing offspring. Fritz
Muller has described a remarkable dimorphic
species of Tanais, in which the male is represented
by two distinct forms, which never graduate
into each other. In the one form the male
is furnished with more numerous smellingthreads,
and in the other form with more powerful
and more elongated chelae or pincers,
which serve to hold the female. Fritz Muller
suggests that these differences between the two
male forms of the same species may have originated
in certain individuals having varied in