86 § 85. 
smaller, Of these, five are elongated quadrilateral plates, placed at the 
base of the lantern, between each two pyramids. The other five, smaller 
and longer, are curved upon the first. 
All these pieces are united by many tendons and muscles to each other, 
and to the neighboring osseous circle which projects inwards from the shell. 
The muscles of mastication are in ten pairs; five of these arise from the 
longest processes of the osseous circle, and are inserted on the pyramids 
below the summit of the lantern. The other five, on the other hand, pass 
from the shortest processes of this circle to the base of the pyramids. 
By this arrangement, when the first five contract and separate the sum- 
mits of the pyramids together with their teeth, the second five, contracting 
also, carry the points of the teeth again together, by separating the bases 
of the pyramids.” ; ; 
In the Clypeastridae, the masticatory apparatus is more simple. It is 
composed of ten unequal, triangular pieces, joined together, V-form, two 
and two. Each of these pieces has in its projecting angle, a furrow in 
which a tooth is fitted. These five jaws are so arranged around the mouth 
that their angles and the points of their teeth meet together in its centre. 
THE ECHINODERMATA. 
§ 85. 
The digestive cavity of the Ophiuridae is only a simple stomachal sac, 
occupying the centre of the hollow dise of their body. 
It is divided by walls projecting inwardly, into many caeca, which never 
extend into the rays.” ; 
There are usually ten of these caeca, which in Astrophyton are subdivided 
into numerous smaller caeca. 
With the Asteroidae, the stomach is large and has a similar situation; 
but it sends off radial caeca into the rays. 
In those species which have an anus, the digestive canal may be divided 
into three parts. The stomach is separated into two chambers by a circu- 
lar, projecting fold. The first of these is the true stomach, and the second 
sends off the radial caeca. A narrow, short rectum, passing off from 
the stomach, forms the third part of this canal, and terminates in an 
anus, situated upon the back of the animal and concealed among points, 
callosities, &c. This rectum has folds which, of a variable length and some- 
times branched, are called the inter-radial caeca, and are situated between 
instead of in the rays. 
In the Comatulinae, this canal consists of a coecum situated at the end 
of a short cesophagus, and which, after a spiral course about the axis of 
the body, terminates in an anus having the form of a short tube projecting 
from the ventral surface not far from the mouth.” 
In Comatula europaea, the axis, around which the digestive canal passes 
1 This apparatus has been minutely described by 
Tiedemann (loc. cit. p. 72, Taf. X. fig. 1, 2), by 
Meckel (Syst. d. vergleich, Anat. IV. p. 56), and 
by Valentin (Monogr. &c. p. 63, Pl. V.). See 
also the beautiful figure by Rymer Jones (Out- 
line of the Anim. King. &c. p. 167, fig. 70, 71). 
2 Agassiz, Monogr. &c. 2¢ Livr. Scutelles. p. 
15, Pl. XID. XTII. XIV. &c. 
1 Konrad, De Asteriarum fabrica, fig. 5. 
2 Meckel, Syst. d. vergleich, Anat. IV. p. 60. 
8 See also Tiedemann (loc. cit. Taf. VII.), whose: 
beautiful figures have been copied everywhere ; 
and the original designs of the digestive cavity of 
Asteracanthion, Archaster, and Culcita, by Mul- 
ler and Troschel (loc. cit. Taf. XI. XII.). : 
4 Upon the digestive canal of Comatula, see 
Heusinger, Zeitschr. f. d. organische Physik. III. 
1829, p. 871, Taf. X. XL. 
