differ in the structure of their chelae. (13. Fritz Muller, Facts and
Arguments for Darwin, 1869, pp. 25-28.) As either chela would
certainly suffice to hold the female, for both are now used for this
purpose, the two male forms probably originated by some having varied
in one manner and some in another; both forms having derived certain
special, but nearly equal advantages, from their differently shaped
organs.
It is not known that male crustaceans fight together for the possession
of the females, but it is probably the case; for with most animals when
the male is larger than the female, he seems to owe his greater size to
his ancestors having fought with other males during many generations.
In most of the orders, especially in the highest or the Brachyura, the
male is larger than the female; the parasitic genera, however, in which
the sexes follow different habits of life, and most of the Entomostraca
must be excepted. The chelae of many crustaceans are weapons well
adapted for fighting. Thus when a Devil-crab (Portunus puber) was seen
by a son of Mr. Bate fighting with a Carcinus maenas, the latter was
soon thrown on its back, and had every limb torn from its body. When
several males of a Brazilian Gelasimus, a species furnished with
immense pincers, were placed together in a glass vessel by Fritz
Muller, they mutilated and killed one another. Mr. Bate put a large
male Carcinus maenas into a pan of water, inhabited by a female which
was paired with a smaller male; but the latter was soon dispossessed.
Mr. Bate adds, if they fought, the victory was a bloodless one, for I
saw no wounds. This same naturalist separated a male sand-skipper (so
common on our sea-shores), Gammarus marinus, from its female, both of
whom were imprisoned in the same vessel with many individuals of the
same species. The female, when thus divorced, soon joined the others.
After a time the male was put again into the same vessel; and he then,
after swimming about for a time, dashed into the crowd, and without any
fighting at once took away his wife. This fact shews that in the
Amphipoda, an order low in the scale, the males and females recognise
each other, and are mutually attached.
The mental powers of the Crustacea are probably higher than at first
sight appears probable. Any one who tries to catch one of the
shore-crabs, so common on tropical coasts, will perceive how wary and
alert they are. There is a large crab (Birgus latro), found on coral
islands, which makes a thick bed of the picked fibres of the cocoa-nut,
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