The life of crustacea / by W.T. Calman.

  • William Thomas Calman
Date:
1911
Catalogue details

Licence: In copyright

Credit: The life of crustacea / by W.T. Calman. Source: Wellcome Collection.

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    as examples of this mode of development. The Woodlice and their immediate allies differ a little from the other members of the division in the fact that the young leave the brood-pouch with the last pair of legs still undeveloped, though in other respects they are like miniature adults. In those Crustacea which have a direct develop- ment without free-swimming larval stages, it is sometimes possible to find traces of such stages in the early development of the embryo. This is shown most clearly, perhaps, in the Opossum Shrimps (Mysidacea). In these the embryo be- comes free from the egg-membrane (or may, in a sense, be said to “ hatch ”) at a very early stage, and lies free within the brood-pouch as a maggot-shaped body, on which three pairs of rudimentary limbs can be made out. The later development shows that these three rudiments correspond to the antennules, antennae, and mandibles, so that the maggot-shaped embryo is, in fact, a disguised nauplius without the power of swimming or of leading an independent existence. In other cases—as, for instance, in the Crayfish, where the earlier stages are confined within the egg-membrane (or “ egg-shell ”)—the nauplius stage, although more difficult to examine, is quite as well marked. Of the other groups of the Malacostraca, the Syn- carida and Leptostraca are hatched in nearly the adult form, but the Stomatopoda have a long series
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