94 THE ECHINODERMATA. §"§> 93, 94. 



§ 93. 



III. Ill 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 

 I?^iwe^?^aea, have there been found proper respiratory openings ; these are 

 four or five papillae, 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 SECKETION. 



§ 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, 3 Quatrefages, Ann. d. So. Nat. loc. cit. p. 64, 



observed by Grube {Mii/ler's Arch. 137, p. 253) PI. V. fig. 1, f. 



upon that of Sipunculus nudua. The same con- 4 The manner in which the water enters into the 



elusion might be drawn from the liquid moved by interior of the Echiuridae is not quite clear to me 



cilia observed by myself in the interior of the ten- from the description of Forbes and Gondsir (Fro- 



taoular lobules of Phascolosoma granulatum. riep''s neue Not. No. 392, p. 277). 



Grube {Mailer^ s Arch. 1837, p. 251, Taf. XI. fig. ' The attention has already been directed to 



2, P.) has seen in Sipunculus nudus the two vesi- these glandular organs, when speaking of the parts 



cles of Poli, communicating with the cavity of the to which they are attached. The calcareous sac, 



tentacular membrane. or stony canal as now understood, of certain Aste- 



1 Muller and Troschel, loc. cit. Taf. IX. X. riae, can scarcely be regarded as organs of secre- 



3 Ekrenberg, Abhandl. d. Berl. Akad. 1835, tion. 

 Taf. Vm. fig. 12, e. ; and Sharpey, Cyclopasdia 

 of Anat. &c. I. p. 615, fig. 298, C. 



* [ End of § 93.] In Echinarachnius and Cly- of the disc, emptying first into a circular tube, anal- 



peaster Agassiz has observed that trachean tubes, ogous to the ch-cular tube of the Discophora, from 



similar to those of the Asteroidae, perform the which extend ramifications into the main cavity of 



funcUon of carrying the water in and out of the the body ; see Compt. rend. 1847. — Ed. 

 body. They are situated chiefly along the margin 



