§ 266. THE CRUSTACEA. 311 



The body of tliese 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, contain chitine. It is covered with a thin layer of dark- 

 colored pigment cells. 



But the valves of the Cirripedia differ essentially from the calcareous 

 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 their 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-ai-ranged septa, 

 into compartments filled with a fibrous substance.**' With Tubicinella. 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 moUusca, 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, PI. X. 2 See Schmidt, loc. cit. p. 60. 



fig. 1), has observed with Balanus pusillus, that 3 See Poli, luc. cit. Tab. IV. fig. 6-10 ; Rapp, 



the Cirripedia, like the other Crustacea, cast olf in fViegmann's Arch. 1841, I. p. 108 ; and Cold- 



their entire sliin at certain seasons. I have my- stream, in the Cyclop, of Anat. loc. cit. p. OSS. 



self often seen this animal deprived of its skm with 4 For Coronula diademi and balaenaris, see 



all the appendages, and even the mantle which Chemnitz, Neues CuncliyUen-CaI)in. VIII. p. 319, 



lines its shell. In captivity, these little animals re- Taf. XCIX. fig. 8-U, S40 ; Lamarck, Ann. du 



peat this process at irregular and often very short RIus. d. Hist. Nat. I. p. 461, PI. XXX. fig. 3, and 



intervals, as in twelve, eight and even five days. Burmeister, Beitrage, &c., p. 34, Taf. I. fig. 2, 3. 



* [ § 265. 1 Witli the Anatifae, the siphon or from the pair of distinct antennae to the fixed sim- 



pedicle corresponds to a pair of antennae in the pie pedicle ; see Dana, Notice of some Genera of 



young; the animal attaches itself by the sucker- Cyclopacea, SsV^iman's Jour. Vol. I. 2°'" Ser. p. 225, 



like disc terminating these organs, before the meta- note, also Rep. on Crustacea, Ex. Exped. of the U. 



morptiosis Ci)mmeiice3, and in a group of these S. p. 1393. — Ed. 

 animals all the ditluront stages may be observed. 



