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Updated: May 3, 2025
The larvæ of barnacles and other more degraded parasitic crustacea are almost exactly like those of Crustacea in general. The embryos of birds have a long tail containing almost or quite as many vertebræ as that of archæopteryx. But most of these never reach their full development but are absorbed into the pelvis, or into the "ploughshare" bone supporting the tail feathers.
I have been trying to realize from memory the particular instincts of those antediluvian animals of the secondary period, which succeeding to the mollusca, to the crustacea, and to the fish, preceded the appearance of the race of mammifers. The generation of reptiles then reigned supreme upon the earth.
Next to the extensive sections of the Stalk-eyed and Sessile-eyed Crustacea, but more nearly allied to the former than to the latter, comes the remarkable family of the Diastylidae or Cumacea. The young, which Kroyer took out of the brood-pouch of the female, and which attained one-fourth of the length of their mother, resembled the adult animals almost in all parts.
It burrows in the loose bottom, or lies in it with its large compound eyes peeping out in search of prey. Its remains form from a third to a fourth of all the buried Cambrian skeletons. With it, swimming in the water, are smaller members of the same family, which come nearer to our familiar small Crustacea. Shell-fish are the next most conspicuous inhabitants.
But the Crustacea exhibit many peculiar features in common with insects, spiders, and centipedes, so that these are grouped into the still larger assemblage or "province" Articulata; and, finally, the relations which these have to worms and other lower animals, are expressed by combining the whole vast aggregate into the sub-kingdom of Annulosa.
In all these detached formations, so diversified in their lithological characters, the remains of the same shells, corals, crustacea, and fish are becoming inclosed; or, at least, a sufficient number must be common to the different localities to enable the zoologist to refer them all to one contemporaneous assemblage of species.
The objection that broad statements of this kind, after all, rest largely on negative evidence is obvious, but it has less force than may at first be supposed; for, as might be expected from the circumstances of the case, we possess more abundant positive evidence regarding Fishes and marine Mollusks than respecting any other forms of animal life; and yet these offer us, through the whole range of geological time, no species ordinally distinct from those now living; while the far less numerous class of Echinoderms presents three, and the Crustacea two, such orders, though none of these come down later than the Palaeozoic age.
But in the highest types, as in the large Crustacea, many of the segments are completely fused together; and the internal organs are no longer uniformly repeated in all the segments. Now the segments of which nations at first consist, lose their separate external and internal structures in a similar manner.
There are only two orders extinct among the 'Crustacea'. There is not known to be an extinct order of these creatures, the parasitic and other worms; but there are two, not to say three, absolutely extinct orders of this class, the 'Echinodermata'; out of all the orders of the 'Coelenterata' and 'Protozoa' only one, the Rugose Corals.
Among Crustacea, the Shrimp-like forms of the earlier geological epochs have become much less conspicuous, while Crabs and Lobsters are now the prominent representatives of the class. Among Mollusks, the Chambered Shells, hitherto so numerous, have become, as they now are, very few in comparison with the naked Cephalopods.
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