The Descent of Man

(2. The 'American Naturalist,' April 1871, p.
119.) The widely distinct Monacanthus scopas
presents a somewhat analogous structure. The
male, as Dr. Gunther informs me, has a cluster
of stiff, straight spines, like those of a comb, on
the sides of the tail; and these in a specimen six
inches long were nearly one and a half inches
in length; the female has in the same place a
cluster of bristles, which may be compared
with those of a tooth-brush. In another species,
M. peronii, the male has a brush like that possessed
by the female of the last species, whilst
the sides of the tail in the female are smooth. In
some other species of the same genus the tail
can be perceived to be a little roughened in the
male and perfectly smooth in the female; and
lastly in others, both sexes have smooth sides.
The males of many fish fight for the possession
of the females. Thus the male stickleback (Gasterosteus
leiurus) has been described as "mad
with delight," when the female comes out of