§^ 75, 76. THE ECHINODERMATA. 79 



§ 75. 



A peculiar calcareous plate (the madreporic plate) is observed upon the 

 <5utaneous skeleton of the Asteroidea and Echinoi'dea. In the last it is 

 always situated in the centre of the dorsal surface, but in the first its 

 position varies. In the proper Asteroidae there are often several, having 

 an excentric dorsal situation ; while in the Ophiuridae^^* it is found upon 

 the ventral surface, and especially in the angle formed by the junction of 

 the two arms with the tortuous mouth. In some Asteroidae a membra- 

 nous sac (stony canal), filled with organized calcareous particles, is attached 

 to this plate ; in others, an articulated calcareous cord stretches obliquely 

 across the body towards the border of the mouth. The use of these parts 

 is not yet positively known. ^-^ 



CHAPTER II. 



MUSCULAR SYSTEM AND ORGANS OF LOCOMOTION. 



§76. 



In the Echinoderms the muscular system is well developed. Its primi- 

 tive fibres are flat, and without transverse striae.*'* 



In the ventral surface, and between each joint of the arms and pin- 

 nulae of the Crinoidea, there are one or two small muscles, antagonistic to 

 which, upon the opposite surface, is an interarticular elastic tissue.'-* 



In the Asteroidea, the interarticular lacunae of the internal skeleton are 

 filled with muscles. '^"' The skin of these animals does not aid the motions 

 of the arms, except by its elasticity. But in the Echinidae the skin 



Duvernaea. The similar hooks found in the sea- 1834, p. 580) has shown that they do not contain or- 

 mud of Vera Cruz have been taken by Ehrenherg dinary calcareous matter, but rather that which is 

 for stony concretions belonging to a sponge, and organized and perforated iii a reticulated manner, 

 figured and named SpongoUthis anchora (Ab- A calcareous cord of a special structure is found la 

 hand. d. Berl. Akad. 1841, p. 32-3, Taf. III. No. Asteracanthion ; see Siebold, Mullar^s Arch. 

 VII. fig. 36). He has also taken the perforated 1836, p. 291, -Taf. X. fig. 14-18 ; and Sharpey, 

 supports of these hooks for an Infusorium with a Cyclop. Anat. &c. loc. cit. II. p. 85, fig. 12, 13, s.* 

 siliceous carapace, described as Dictyocha splen- 1 According to Wagner (Muller's Arch. 1835, 

 dens (Ibid. fig. 35). But, more lately, he has p. 319), the Echinoderms do not have transversely 

 parceived their true nature (Ibid. p. 407, 44;3). striated muscles. This has been confirmed by 

 The discovery of analogous cutaneous organs in the Müller (Abhand. d. Berl. Akad. loc. cit. p. 214, Taf. 

 inarl near Streitberg, by Count Münster (Beitr. IV. fig. 9) in the genera, Pentacrinus and Coma- 

 z. Petrefak. Hft. VI. 1843, p. 92, 96, Taf. IV. fig. tula. For my own part, I have failed to perceive 

 .9), is very interesting, since it shows the antedilu- them in Echinus, Asterias, Ophiurus, Uolothu- 

 vian existence of Synapta. ria, and Sipunculus. yalentin (Monogr. loc. cit. 

 Beside the cutaneous corpuscles of carbonate of ' p. 101, PI. VIII. fig. 153-155) asserts to have 

 lime, Quatrefages (loc. cit. p. 36, PI. III. fig. 15) seen striae upon the fibres of the masticatory, spin- 

 has found others which are of a spherical form in ous and anal muscles of Echinus ; and Quatre- 

 the skin of Synapta Duvernaea ; and, as they fages (Ann. de. Sc. Nat. loc. cit. p. 43, PI. UX 

 have protractile filaments, he compares them to fig. 17) has observed transverse wrinkles during the 

 nettling organs. contraction of the longitudinal muscles of Synapta. 



1 Astrophyton. 2 Müller, Abhand. d. Berl. Akad. loc. cit. p. 214, 



2 These parts are found in Astropecten. Ac- 220, Taf. II. fig. 8, 12. 



cording to Tiedeinann (loc. cit. p. 54), they furnish S The interarticular muscular layer of the 

 the necessary calcareous matter tor the skeleton of Asteroidae has been accurately described by 

 the Asteroidae. But Ehrenberg (^Muller's Arch. Meckel (System d. vergleich. Anat. III. p. 14). 



* [ § 75, note 2.] See, for further details on this stone-canal with the Ophiuridae, Müller, Arch. I860, 

 p. 122. — Ed. 



