Associated with, or in the immediate vicinity of
the two species of Melita, live two species of Allorchestes, the pairs
of which are met with almost more numerously than the single animals,
and yet their females show no trace of the above-mentioned processes of
the coxal lamellae.
These cases, I think, must be brought to bear against the conception
supported with so much genius and knowledge by Agassiz, that species are
embodied thoughts of the Creator; and, with these, all similar instances
in which arrangements which would be equally beneficial to all the
species of a group are wanting in the majority and only conferred upon a
few special favourites, which do not seem to want them any more than the
rest.
CHAPTER 5. RESPIRATION IN LAND CRABS.
Among the numerous facts in the natural history of the Crustacea upon
which a new and clear light is thrown by Darwin's theory, besides the
two forms of the males in our Tanais and in Orchestia Darwinii, there is
one which appears to me of particular importance, namely, the character
of the branchial cavity in the air-breathing Crabs, of which,
unfortunately, I have been unable to investigate some of the most
remarkable (Gecarcinus, Ranina). As this character, namely, the
existence of an entrance behind the branchiae, has hitherto been
noticed, even as a fact, only in Ranina, I will go into it in some
detail.
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