94 



THE ECHINODERMATA. 



f.*^ 93, 94. 



§ 93. 



III. In nearly all the Echinoderms, as has been seen, all the viscera are 

 bathed with water which certainly aifects 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 

 Dmiernaea, 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 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 (Muller^s Arch. 137, p. 253) 

 upon that of Sipunculus nudus. The same con- 

 clusion might be drawn from the liquid moved by 

 cilia oV>served by myself in the interior of the ten- 

 tacular lobules of Pliascolosoma granulattnn. 

 Grube (Mutter's Arch. 1837, p. 251, Taf. XI. fig. 

 2, P.) has seen in Sipunculus nudus the two vesi 

 cles of Poli, communicating with the cavity of the 

 tentacular membrane. 



1 Mutter and Troschel, loc. cit. Taf. IX. X. 



2 E/irenber/f, Abhandl. d. Berl. Akad. 1835, 

 Taf. Vtll. fig. 12, e. ; aM Stinrpey, Cyclopsedia 

 of Anat. &c. I. p. 615, fig. 2«8, C. 



* [ End of § 93.] In Echinaraclinius and Cty- 

 peaster Af^assiz has observed that trachean tubes, 

 similar to those of the Asteroidae, perform the 

 function of carrying the water in and out of the 

 body. They are situated chiefly along the margin 



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

 PI. V. fig. 7, f. 



4 The manner in which the water enters into the 

 interior of the Echluridae is not quite clear to me 

 from the description of Forbes and Gondsir (^Fro- 

 riep\s neue Not. No. 392, p. 277). 



I 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 Ito the main cavity of 

 the body ; see Compt. rend. 1847. — Ed. 



