The Descent of Man

the spawning-season than at any other time."
The species of Geophagus act in the same manner;
and in this genus, a conspicuous protuberance
becomes developed on the forehead of
the males during the breeding-season. With the
various species of Chromids, as Professor
Agassiz likewise informs me, sexual differences
in colour may be observed, "whether they lay
their eggs in the water among aquatic plants, or
deposit them in holes, leaving them to come
out without further care, or build shallow nests
in the river mud, over which they sit, as our
Pomotis does. It ought also to be observed that
these sitters are among the brightest species in
their respective families; for instance, Hygrogonus
is bright green, with large black ocelli,
encircled with the most brilliant red." Whether
with all the species of Chromids it is the male
alone which sits on the eggs is not known. It is,
however, manifest that the fact of the eggs
being protected or unprotected by the parents,
has had little or no influence on the differences