THE ECHINODERMATA. 
§ 75. 
A peculiar calcareous plate (the madreporic plate) is observed upon the 
cutaneous skeleton of the Asteroidea and Echinoidea. 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. 
§$ 75, 76. 79 
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 foynd in the. sea- 
mud of Vera Cruz have been taken by Ehrenberg 
for stony concretions belonging to a sponge, and 
figured and named Spongolithis anchora (Ab- 
hand. d. Berl. Akad. 1841, p. 323, Taf. III. No. 
VII. fig. 36). He has also taken the perforated 
supports of these hooks for an Infusorium with a 
siliceous carapace, described as’ Dictyocha splen- 
dens (Ibid. fig. 35). But, more lately, he. has 
perceived their true nature (Ibid. p. 407, 443). 
‘The discovery of analogous cutaneous organs in the 
marl near Streitberg, by Count Munster (Beitr. 
z. Petvefak. Hft. VI. 1843, p. 92, 96, Taf. IV. fig. 
9), is very interesting, since it shows the antedilu- 
vian existence of Synapta. 
Beside the cutaneous corpuscles of carbonate of 
lime, Quatrefages (loc. cit. p. 36, Pl. III. fig. 15) 
has found others which are of a spherical form in 
the skin of Synapta Duvernaea; and, as they 
have protractile filaments, he compares them to 
nettling organs. 
1 Astrophyton. 
2These parts are found in ‘Astropecten. Ac- 
cording to Tiedemann (loc. cit. p. 54), they furnish 
the necessary calcareous matter for the skeleton of 
the Asteroidae. But Ehrenberg (Miuller’s Arch. 
1834, p. 580) has shown that they do not contain or= 
dinary calcareous matter, but rather that which is 
organized and perforated in a reticulated manner. 
A calcareous cord of a special structure is found in” 
Asteracanthion ; see Siebold, Muller’s Arch. 
1836, p. 291, Taf. X. fig, 14-185 and Sharpey, 
Cyclop. Anat. &c. loc. cit. II. p. 85, fig. 12, 18, s.* 
1 According to Wagner (Miiller’s Arch. 1835, 
p. 819), the Echinoderms do not have transversely 
striated muscles. This has been confirmed by 
Miller (Abhand. d. Berl. Akad. loc. cit. p. 214, Taf. 
IV. fig. 9) in the genera Pentacrinus and Coma- 
tula. For my’ own part, I have failed to perceive 
them in- Echinus, Asterias, Ophiurus, Holothu- 
ria, and Sipunculus. Valentin (Monogr. loc. cit. 
p. 101, Pl. VIII. fig. 153-155) asserts to have 
seen striz upon the fibres of the masticatory, spin- 
ous and anal muscles of Echinus ;, and Quatre- 
Jages (Ann. de. Sc. Nat. loc. cit. p. 43, Pl. IIL 
fig. 17) has observed transverse wrinkles during the 
contraction of the longitudinal muscles of Synapta. 
2 Miller, Abhand. a. Berl. Akad. loc. cit. p. 214, 
220, Taf. II. fig. 8, 12.. 
8 The interarticular muscular layer of the 
Asteroidae has been accurately described by 
Meckel (System d. vergleich. Anat. IIT. p. 14). 
* [§ 75, note 2.] See, for further details on this stone-canal with the Ophiuridae, Muller, Arch. 1860,. 
p. 122.—Ep. 
