$ 266. THE CRUSTACEA. sli 
The body of these animals, as well as its articulated appendages, are 
enclosed in a cutaneous skeleton containing the chitine; and, moreover, is 
enveloped in a peculiar mantle having, externally, calcareous plates which 
vary in number and are so united together as to be movable in some 
species, and fixed in others. With the Lepadea, the mantle is prolonged 
into a kind of siphon.* Not only this mantle, but also its ligaments 
uniting the movable pieces of the shell and the siphon, are composed of a 
lamellated tissue analogous to that of the proper cutaneous skeleton, and 
like it also, coutain chitine. It is covered with a thin layer of dark- 
colored: pigment cells. 
But the valves of the Cirripedia differ essentially from the caleareous 
shell of the other Crustacea. In the first place, they have no participation 
in the moulting, to which the cutaneous skeleton and the mantle are regu- 
larly subjected ;® then again, their structure and chemical composition 
resemble that of many of the Bivalvia.” The valves of the Balanoidea 
form the only exception in this respect. They are traversed. in part, by 
numerous parallel tubes, dilated at tucir inferior or their external portion, 
which pursue a vertical course in the vertical valves, but are radiated in 
the horizontal plate. ‘These tubes, which are wanting in the movable oper- 
cula of these shells and in the transversely-striated valves which, in the 
genus Balanus, are intercalated between the longitudinally-striated ones, 
are often laterally compressed, and their interior has imperfect longitudinal 
septa, or is even divided into several chambers by transverse partitions. 
The horizontal plate which forms the base of the shell, is perforated cen- 
trally, and hollowed on its under surface, with the genus Coronula. This 
cavity is divided, by numerous vertical and symmetrically-arranged septa, 
into compartments filled with a fibrous substance. With Tudicinedia, this 
plate is entirely wanting, and is replaced by a fibrous substance. This 
fibrous matter, by which Coronula and Tubicinella are fixed firmly to 
foreign bodies, is comparable to the pedicle of the Lepadea, which has 
become internal and overgrown by the shell. 
The increase of the shells of Cirripedia follows the same laws as that 
with the bivalve or multivalve mollusca, judging from the course of the 
lines of growth which they present. 
§ 266. 
The form and number of the different segments of the cutaneous skele- 
ton, which are sometimes extraordinarily developed, and sometimes equally 
1 Thompson (Zool. Research, &c. p. 79, Pl. X. 
fig. 1), has observed with Balanus pusilius, that 
the Cirripedia, like the other Crustacea, cast off 
their entire skin at certain seasons. I have my- 
self often seen this animal deprived of its skin with 
all the appendages, and even the mantle which 
lines its shell. In captivity, these little animals re- 
peat this process at irregular and often very short 
intervals, as in twelve, eight and even five days. 
* | §265.] With the Anatifae, the siphon or 
pedicle corresponds to a pair of antennae in the 
young ; the animal attaches itself by the sucker- 
like disc terminating these organs, before the meta- 
morphosis commences, and in a group of these 
animals all the different stages may be observed, 
2 See Schmidt, loc. cit. p. 60. 
8 See Poli, loc. cit. Tab. IV. fig. 6-10; Rapp, 
in Wiegmann’s Avch. 1841, I. p. 168 ; and Cold- 
stream, in the Cyclop. of Anat. loc. cit. p. 685. 
4 For Coronula diademz and ba/aenaris, see 
Chemnitz, Neues Conchylien-Cabin. VUL. p. 319, 
Taf. XCIX. fig. 844, 846; Lamarck, Ann. du 
Mus. d. Hist. Nat. I. p. 461, Pl. XXX. fig. 3, and 
Burmeister, Beitrage, &c., p. 34, Taf. 1. fig. 2, 3. 
from the pair of distinct antennae to the fixed sim- 
ple pedicle ; sce Dana, Notice of some Genera of 
Cyclopacea, Sidliman’s Jour. Vol. I. 294 Ser. p. 225, 
note, also Rep. on Crustacea, Ex. Exped. of the U. 
8. p. 1893. — Ep. 
