As far as structure is concerned, the two sexes of many
animals and of some plants differ to an extreme degree; and in both kingdoms the
same species may consist of males, females, and hermaphrodites. Certain
hermaphrodite cirripedes are aided in their reproduction by a whole cluster of
what I have called complemental males, which differ wonderfully from the
ordinary hermaphrodite form. With ants we have males and females, and two or
three castes of sterile females or workers. With Termites there are, as Fritz
Muller has shown, both winged and wingless males and females, besides the
workers. But in none of these cases is there any reason to believe that the
several males or several females of the same species differ in their sexual
powers, except in the atrophied condition of the reproductive organs in the
workers of social insects. Many hermaphrodite animals must unite for
reproduction, but the necessity of such union apparently depends solely on their
structure. On the other hand, with heterostyled dimorphic species there are two
females and two sets of males, and with trimorphic species three females and
three sets of males, which differ essentially in their sexual powers. We shall,
perhaps, best perceive the complex and extraordinary nature of the marriage
arrangements of a trimorphic plant by the following illustration.
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