THE ECHINODERMATA. $$ 93, 94. 
§ 93. 
III. In nearly all the Echinoderms, as has been seen, all the viscera are 
bathed with water which certainly affects their delicate blood-vessels. It 
is very probable that from ciliated epithelium covering the entire cavity of 
the body and the viscera this water circulates in a definite manner. It 
is rejected at last through many respiratory openings, through which also 
fresh water is introduced. * : 
In the Ophiuridae, there are in each inter-radial space two or four large 
‘openings of this kind, leading into the cavity of the body.” 
In the Asteroidae, water passes freely in and out the cavity of the 
body, through small contractile trachean tubes, which have been known for 
a ‘long time, and which are very numerous upon the back. They are cov- 
ered within and without with ciliated epithelium, and have an opening at 
their extremity.” As yet it is unknown how the cavity of the body of 
the Echinoidea and Holothurioidea receives the water. Only in Synapta 
Duvernaea, have there been found proper respiratory openings; these are 
four or five papille, covered with cilia, concealed at the base of the oral 
tentacles, and connecting with the cavity of the body through a narrow 
canal.® In the Sipunculidae, the water is received through an opening 
at the posterior end of the body.“* 
CHAPTER VIII. 
ORGANS OF SECRETION, 
§ 94. 
The Echinoderms appear to have special organs of secretion. In differ- 
ent parts of the body there are glandular organs, the real nature of which, 
however, has not yet been determined.” 
‘by the presence of delicate and tortuous vessels, 
observed by Grube (Miiller’s Arch. 137, p. 253) 
wpon that of Sipunculus nudus. The same con- 
-clusion might be drawn from the liquid moved by 
‘cilia Sbserved by myself in the interior of the ten- 
itacular lobules of Phascolosoma granulatum. 
Grube (Muller’s Arch. 1837, p. 251, Taf. XI. fig. 
2, P.) has seen in Sipunculus nudus the two vesi 
cles of Pol, communicating with the cavity of the 
tentacular membrane. 
1 Muller and Troschel, loc. cit. Taf. IX. X. 
2 Ehrenberg, Abhandl. d. Berl. Akad. 1835, 
Taf. VITI. fig. 12, e.; and Sharpey, Cyclopedia 
of Anat. &c. I. p. 616, fig. 298, C. 
* { End of § 93.] In Echinarachnius and Cly- 
peaster Agassiz has observed that trachean tubes, 
similar to those of the Asteroidae, perform the 
function of carrying the water in and ont of the 
dody. They are situated chiefly along the margin 
3 Quatrefages, Ann. d. So. Nat. loc. cit. p. 64, 
Pl. V. fig. 7, f. 
4 The manner in which the water enters into the 
interior of the Echiuridae is not quite clear to me 
from the description of Forbes and Goodsir (Fro- 
riep’s neue Not. No. 392, p. 277). 
\The attention has already been directed to 
these glandular organs, when speaking of the parts 
to which they are attached. The calcareous sac, 
or stony canal as now understood, of certain Aste- 
riae, can scarcely be regarded as organs of secre- 
tion. 
of the disc, emptying first into a circular tube, anal- 
ogous to the circular tube of the Discophora, from 
which extend ramifications i tto the main cavity of 
the body ; see Compt. rend. 1847, — Ep. 
