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In these also the brood bursts out in the Nauplius-form, and speedily strips off its earliest larva-skin which is distinguished by no peculiarities worth noticing. A pair of similar filaments spring, in the larvae of the Cirripedia and Rhizocephala, directly from the brain. Nauplius of Sacculina purpurea, shortly before the second moult, magnified 180 diam.
All this is wanting in the young Rhizocephala. The Nauplii of the Cirripedia have to undergo several moults whilst in that form; the Nauplii of the Rhizocephala, being astomatous, cannot of course live long as Nauplii, and in the course of only a few days they become transformed into equally astomatous "pupae," as Darwin calls them.
The ANNULOSA. The Carboniferous Insecta and Arachnida are neither less specialized, nor more embryonic, than those that now live, nor are the Liassic Cirripedia and Macrura; while several of the Brachyura, which appear in the Chalk, belong to existing genera; and none exhibit either an intermediate, or an embryonic, character.
And this, strange as it may appear at the first glance, seems to me scarcely doubtful. It is true that the act of adhesion of the Rhizocephala has never yet been observed, but it is more than probable that they attach themselves, just like the Cirripedia, by means of the antennae, and that therefore the points of attachment in the two groups indicate homologous parts of the body.
Smith's theory therefore is that the action of the testes in metabolism is rather to take something from the blood than to add something to it, and that it is this subtractive effect which influences the development of somatic sexual organs. Sacculina is one of the Cirripedia, and therefore allied to the Barnacles.
As for the articulates, in his notes Conseil has very appropriately divided them into six classes, three of which belong to the marine world. These classes are the Crustacea, Cirripedia, and Annelida.
Darwin regards them as forming a peculiar sub-class equivalent to the Podophthalma, Edriophthalma, etc. This appears to me to be most convenient. I would not combine the Rhizocephala with the Cirripedia, as Liljeborg has done, but place them in opposition as equivalent, like the Amphipoda and Isopoda.
To-day as I was opening a specimen of Lepas anatifera in order to compare the animal with the description in Darwin's 'Monograph on the Subclass Cirripedia, I found in the shell of this Cirripede, a blood-red Annelide, with a short, flat body, about half an inch long and two lines in breadth, with twenty-five body-segments, and without projecting setigerous tubercles or jointed cirri.
My work on the Cirripedia possesses, I think, considerable value, as besides describing several new and remarkable forms, I made out the homologies of the various parts I discovered the cementing apparatus, though I blundered dreadfully about the cement glands and lastly I proved the existence in certain genera of minute males complemental to and parasitic on the hermaphrodites.
In October, 1846, I began to work on 'Cirripedia. When on the coast of Chile, I found a most curious form, which burrowed into the shells of Concholepas, and which differed so much from all other Cirripedes that I had to form a new sub-order for its sole reception. Lately an allied burrowing genus has been found on the shores of Portugal.
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