The Descent of Man

moulting, she could then be seized with impunity.
[Fig.8. Orchestia Darwinii (from Fritz Muller),
showing the differently- constructed chelae of
the two male forms.]
Fritz Muller states that certain species of Melita
are distinguished from all other amphipods by
the females having "the coxal lamellae of the
penultimate pair of feet produced into hooklike
processes, of which the males lay hold with
the hands of the first pair." The development of
these hook-like processes has probably followed
from those females which were the most
securely held during the act of reproduction,
having left the largest number of offspring.
Another Brazilian amphipod (see Orchestia
darwinii, Fig. 8) presents a case of dimorphism,
like that of Tanais; for there are two male
forms, which differ in the structure of their chelae.
(13. Fritz Muller, 'Facts and Arguments for
Darwin,' 1869, pp. 25-28.) As either chela would