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It need hardly be mentioned that the sexual peculiarities are not yet developed, and that in the males the hand-like enlargements of the anterior ambulatory feet and the copulatory appendages are still deficient. To the question, how far the development of Ligia is repeated in the other Isopoda, I can only give an unsatisfactory answer.
Of fishes, the most remarkable was a Torpedo, with the back of a reddish brown, and smooth; and a Callorhynchus antarcticus: the latter may very well remain in the class of Chimæra. Of crustaceæ, we collected three Canceres, a Portunus, a Porcellana, a Sphæroma, and a Ligia. The dry land along the coast is extremely poor in insects.
It is evident that the larva stands essentially in the grade of Zoea. Less varied than that of the Stalk-eyed Crustacea is the mode of development of the Isopoda and Amphipoda, which Leach united in the section Edriophthalma, or Crustacea with sessile eyes. Embryo of Ligia in the egg, magnified 15 diam.
We may see, without further discussion, how the representation given by Claus of the development of the Copepoda may pass almost word for word as the primitive history of those animals; we may find in the Nauplius-skin of the larvae of Achtheres and in the egg-like larva of Cryptophialus, precisely similar traces of a transition towards direct development, as were presented by the Nauplius-envelope of the embryos of Mysis and the maggot-like larva of Ligia, etc.
The dorsal surface of the Slater is united to the larval skin a little behind the head. At this point, when the union has been dissolved a little before the change of skin, there is a foliaceous appendage, which exists only for a short time, and disappears before the young Slater quits the brood-pouch of the mother. Maggot-like larva of Ligia, magnified 15 diam. R remains of the egg-membrane.
We might urge that, according to this proposition, provisional organs as the first produced must exceed the later-formed permanent organs in importance. But let us stick to the Crustacea. In Polyphemus Leydig finds the first traces of the intestinal tube even during segmentation. In Mysis a provisional tail is first formed, and in Ligia a maggot-like larva-skin.
In Cassidina also the first larval skin without appendages is easily detected; it is destitute of the long tail, but is strongly bent in the egg, as in Ligia, and consequently cannot be mistaken for an "inner egg-membrane." This interpretation is by no means a happy one.
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