“ The body is indistinctly segmented, and is enveloped in a fold of the integument, usually with calcareous plates. The anterior antennae are fused with the anchoring attachment, whilst the posterior pair is vestigial, and the appendages of the mouth and body present various degrees of degeneration and specialization. ”

“ THYROSTRACA, an order of Crustacea, comprising barnacles, acorn shells and some allied degenerate parasites. The embryos are free-swimming, active forms, but in adult life the animals are fixed head downwards, and are very degenerate. ”

“ Thyrostraca genuina.—It is with these that Darwin’s classical treatises (Ray Soc. and Palaeont. Soc., 1851–1854) are almost exclusively concerned. Therein an order Thoracica comprehends the pedunculate Lepadidae, together with the operculate and sessile Balanidae and Verrucidae; a single species without cirrhi constitutes the order Apoda; and a single species with only three pairs of cirrhi the order Abdominalia. Within the last Kochlorine (Noll, 1872) with two species, and Lithoglyptes (Aurivillius, 1892) with three species, have since been included. ”

“ Thyrostraca anomala.—This section comprises Darwin's Apoda, the footless, Lilljeborg's Suctoria, called by Fritz Müller the Rhizocephala or rootlet-headed, and the group to which Lacaze-Duthiers gave the alternative names Ascothoracida, sac-bodied or Rhizothoracida, rootlet-bodied. For the present these names may be dispensed with in favour of their equivalents, the three families Proteolepadidae, Sacculinidae and Lauridae. The first is still limited to the single genus and species Proteolepas bivincta (Darwin) , parasitic within the sac of another cirripede. ”

“ The second family, discussed by Delage, Giard, Kossmann and others, has no dearth of genera and species, though about several of them the information is scanty. Almost all of them are parasitic on other crustaceans. Sphaerothylacus polycarpus (Sluiter, 1884) has an ascidian for its host. Sarcotaces (Olsson, 1872) has two species parasitic in fishes. But these exceptional and dubious forms do not obtain nutriment by sending rootlets in a rhizocephalous manner into their patrons. ”

“ The cirripede, which has an elastic peduncle, a crested capitulum, but no valves, and the first cirrhi longer than the rest, should stand near Eremolepos, the name given by Weltner in place of the preoccupied Gymnolepas (Aurivillius) . In the genus Scalpellum, S. giganteum, Gruvel (Trans. Linn. Soc., 1901) disputes with S. stearnsii (fig. 2) , Pilsbury, 1890, which shall be accounted the greater. The latter is threatened with a new generic name (Chun, Aus den Tiefen des Weltmeeres, 1900, p. 502) .
The horizontal distribution of barnacles over all seas is fully explained by Darwin. ”