$ 84. THE ECHINODERMATA. 85 
which, by their contraction, is pressed into the cavity of the tentacles for 
Jubrication.@ 
The retraction of the tentacles is due in part to their own contractility, 
and in part to the numerous muscles, which, arising from the internal sur- 
face of the cavity of the body, are inserted into the osseous circle. By 
these means, it, together with the tentacles, can be retracted into the 
body. With the Sipunculidae the tentacular apparatus consists of a 
fringed border on the margin of the mouth, which is also provided 
with vesicles. In Sipunculus, and Phascolosoma, there are four long 
muscles, which, arising from the internal surface of the body, pass on to the 
mouth, and are retractors of the tentacular membrane.” It is possible 
that these oral tentacles serve not only as prehensile organs of food, but 
also as those of locomotion and respiration.© 
. § 84. 
The mouth of the Comatulinae presents nothing remarkable; but with 
the Asteroidae, it is covered with hard papille, projecting from its corners 
and angles.. In the Ophiuride, the inverted angles are covered with hard 
papillae, while the everted ones have calcareous teeth, between which are 
concealed soft cylindrical tentacles. Immediately behind all of these, the 
entrance of the stomach is indicated by a membranous sphincter. In the 
Asteroidae, however, this is wanting, there being a short cesophagus leading 
directly into the stomach. 
With the Echinoidea, and Holothurioidea, the mouth has a soft circular 
lip, between which, with the Hchinidae, and with the Clypeastridae, pro- 
ject the points of enamelled teeth. ; 
The mouth of the Hchinidae, and Clypeastridae, has a very remarkable 
masticatory apparatus. In the first, the calcareous basis which supports the 
teeth has long been known as Aristotle’s lantern. This conical basis is 
divided into a base and summit; the first being the superior part of the 
animal itself, while the second is formed by points of teeth: projecting 
from the mouth. It is, moreover, composed of fifteen pieces, five of which 
are three-sided, hollow pyramids, and so adjusted that they touch each 
other by their plane surfaces, presenting externally the third surface which 
is convex. This last has internally a longitudinal furrow, in which is fitted a 
very long, narrow and slightly-curved tooth. Beside these five principal 
pieces, which form the jaws of Echinus, there are two other kinds, much 
2 These vesicles are found in Ho/othuria and 
Chirodota; sve Tiedemann, loc. cit. Tab. IT. fig. 
4, e. 6, i. ; also the Catalogue of the Museum, Lon- 
don, &c., IV. Pl. XLIX. fig. 1, 2 (Holothuria tubu- 
Zosa) ; and the Atlas Zool. du Voyage de l’Astrolabe. 
Zoophytes, Pl. VIII. fig. 3 (Chirodota fusca). 
In Pentacta doliolum, I have found only a single 
cylindrical vesicle fixed to the circle of tentacles. 
In Synapta Duvernaea, (Quatrefages Ann. d. 
Sc. Nat. loc. cit.), these vesicles are entirely want- 
ing. 
Cuvier (Anat. Comp. V. p. 454) and other anat- 
omists (see Grant, Outlines, &c., p. 333) have 
erroneously taken these parts for salivary organs. 
They do not communicate with the digestive canal, 
but connect freely with the circulatory and respir- 
atory systems,—a point, therefore, to which we 
shall further allude hereafter. 
3 In Pentacta, there are five large cylindrical 
muscles arising from the subcutaneous longitudinal 
ones, and inserted into the osseous circle ; — they 
are special retractors of the tentacles ; see Meckel, 
System d. vergleich, Anat. IV. p. 62. 
4 Tam inclined to regard as tentacular the two 
vesicles of Poli, in Sipunculus; and of which 
Delle Chiaje (Memor. &c. Tav. I. fig. 6, d.) per- 
ceived only one, although Grube (Muller’s Arch. 
1837, p. 251, Taf. XI. fig. 2, P.) has seen them 
both fixed in a space circumscribed by the tentac- 
ular membrane. 
5 Grube, Ibid, p. 241, Taf. XI. fig. 1, u. 2, m. m.3 
and Delle Chiaje, Memor. &c. Tav. I. fig. 3. 
6 The oral tentacles of Synapta Duvernaea, 
which, according to Quatrefages (loc. cit. p. 63, 
Pl. IV. fig. 1), have suckers on their internal sur- 
face, are certainly used as locomotive organs. 
