and even upon mountains of a thousand feet in height, such as O.
tahitensis, telluris, and sylvicola), its male differs still more from
all known species by the powerful chelae of the second pair of feet.
Orchestia gryphus, from the sandy coast of Monchgut, alone presents a
somewhat similar structure, but in a far less degree; elsewhere the form
of the hand usual in the Amphipoda occurs. Now there is a considerable
difference between the males of this species, especially in the
structure of these chelae--a different so great that we can scarcely
find a parallel to it elsewhere between two species of the genus--and
yet, as in Tanais, we do not meet with a long series of structures
running into one another, but only two forms united by no intermediate
terms (Figures 8 and 9). The males would be unhesitatingly regarded as
belonging to two well-marked species if they did not live on the same
spot, with undistinguishable females. That the two forms of the chelae
of the males occur in this species is so far worthy of notice, because
the formation of the chelae, which differs widely from the ordinary
structure in the other species, indicates that it has quite recently
undergone considerable changes, and therefore such a phenomenon was to
be expected in it rather than in other species.

(FIGURES 8 AND 9. The two forms of the chelae of the male of Orchestia
Darwinii, magnified 45 times.)

I cannot refrain from taking this opportunity of remarking that (so far
as appears from Spence Bate's catalogue), for two different kinds of
males (Orchestia telluris and sylvicola) which live together in the
forests of New Zealand, only one form of female is known, and hazarding
the supposition that we have here a similar case. It does not seem to me
to be probable that two nearly allied species of these social Amphipoda
should occur mixed together under the same conditions of life.