It is far from the intention of these pages to enter
upon a general refutation of this theory of adaptation. Indeed there is
scarcely anything essential to be added to the many admirable remarks
that have been made upon this subject since the time of Spinoza. But
this may be remarked, that I regard it as one of the most important
services of the Darwinian theory that it has deprived those
considerations of usefulness which are still undeniable in the domain of
life, of their mystical supremacy. In the case before us it is
sufficient to refer to the Gelasimus of the mangrove swamps, which
shares the same conditions of life with various Grapsoidae and yet does
not agree with them, but with the arenicolous Ocypoda.
CHAPTER 6. STRUCTURE OF THE HEART IN THE EDRIOPHTHALMA.
Scarcely less striking than the example of the air-breathing Crabs, is
the behaviour of the heart in the great section Edriophthalma, which may
advantageously be divided, after the example of Dana and Spence Bate,
only into two orders, the Amphipoda and the Isopoda.
In the Amphipoda, to which the above-mentioned naturalists correctly
refer the Caprellidae and Cyamidae (Latreille's Laemodipoda), the heart
has always the same position; it extends in the form of a long tube
through the six segments following the head, and has three pairs of
fissures, furnished with valves, for the entrance of the blood, situated
in the second, third, and fourth of these segments.
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