The difference of the sexes which, in the Gammarinae is usually
expressed chiefly in the structure of the anterior feet (gnathopoda, Sp.
Bate) and in the Hyperinae in the structure of the antennae, is often so
great that males and females have been described as distinct species,
and even repeatedly placed in different genera (Orchestia and Talitrus,
Cerapus and Dercothoe, Lestrigonus and Hyperia) or even families
(Hyperines anormales and Hyperines ordinaires). Nevertheless it is only
developed when the animals are nearly full-grown. Up to this period the
young resemble the females in a general way, even in some cases in which
these differ more widely than the males from the "Type" of the order.
Thus in the male Shore-hoppers (Orchestia) the second pair of the
anterior feet is provided with a powerful hand, as in the majority of
the Amphipoda, but very differently constructed in the females. The
young, nevertheless, resemble the female. Thus also,--and this is an
extremely rare case,* (* "I know of no case in which the inferior
(antennae) are obsolete, when the superior are developed," Dana.
(Darwin, 'Monograph on the Subclass Cirripedia, Lepadidae' page
15.)--the females of Brachyscelus are destitute of the posterior (or
inferior) antennae; the male possesses them like other Amphipodae; in
the young I, like Spence Bate, can find no trace of them.
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