<$, 92. 



THE ECHINODERMATA. 



93 



trunks from this oral ring pass along the furrows of the rays close to their 

 external surface. The ambulacral vesicles into which their lateral 

 branches open, are sometimes simple/*' or, from a kind of sulcation, have a 

 heart-like form.'^' 



In the Echinoidea, the oral ring wants the pyriforra appendages,'"' and 

 its main trunks pass along the internal wall of the shell. The am'julacral 

 vesicles of the oral membrane are conical ; but the others are flattened, 

 overlap each other in a tile-like manner,"'^' and have a distinct branchial, 

 vascular network.'*" 



The aqueous oral ring of the Holothurinae has hollow appendages (ten- 

 tacular vesicles) projecting into the cavity of the body.'"' It has also, in 

 many species, a larger, longer, and sometimes double, coecal vessel {Am- 

 pulla Polia?ia).^^°' Opposite the tentacular vesicles, the ring sends off' to 

 the oral tentacles, vessels which are often arborescent and comparable to 

 external branchiae ;'^^' while, between these vesicles, arise five other vessels 

 which descend along the internal surface of the body. As usual, they send 

 off lateral branches to the generally very small ambulacral vesicles. ''-' 



In a few species only of the Synaptinae, the aquiferous ring has hollow 

 appendages. '^^' From it pass off' vessels both to the tentacles and to the 

 sides of the body. As the ambulacra are here absent, the five main trunks 

 do not give off lateral branches.'"' 



In the Sipunculo'idea, the aquiferous system is least developed. As yet 

 there has been found only a liquid moved by vibratile cilia in the doubly- 

 laminated cavity of the lobulated tentacles of the Sipunculidae. With 

 this cavity, two vesicles of Poll communicate, thus indicating the presence 

 of an aquiferous system."^' 



last species they are only slightly developed ; in 

 Astropecten. aurantiacus there are three to seven 

 vesicles, opening by a common duct into each of 

 the five angles of the aqueous vascular ring ; see 

 Delle C/iiaje, loc. cit. II. p. 296 ; Tiedemann, loc. 

 cit. p. 52, Taf. VIII. ; Konrad, loc. cit. fig. 3 ; and 

 Meckel, Syst. d. vergleich. Anat. V. p. 32. Hei-e 

 should be mentioned also the glandular corpuscles 

 which are attached to the aqueous vascular ring, 

 and which resemble in some respects the glandular 

 organs of the vascular sanguineous rings of Echi- 

 nus, pointed out by Valetitin ; see Delle Chiaje, 

 loc. cit. II. Tav. XXI. fig. 12, 14 ; Tiedemann, 

 loc. cit. Taf. VIII. o. o., or fVagner, Icon. zoot. 

 Tab. XXXII. fig. 2, m. 



4 Ophidiaster, Asteracant/iion. Luidia ; see 

 Müller and Troschel, loc. cit. Taf. XI. fig. i. 



5 Astropecten ; see Konrad, loc. cit. fig. 4. I 

 am not yet settled upon the question whether the 

 aquiferous system of the Asteroidae is filled by the 

 extremity of the ambulacra, or by the oral ring. I 

 have not been able to convince myself of the pres- 

 ence of an opening at the extremity of these first. 



6 Delle Chiaje (loc. cit. Tav. XXVI.) has given 

 very detailed figures of the aquiferous system of 

 Echinus and Spatangus ; but he has confounded it 

 with the sanguinqpus vessels of the intestinal canal. 



^ yalentin, Mouogr. &c. PI. CXXXIV.— 

 CXXXVI. 



8 The branchial vessels ramifying upon the flat- 

 tened ambulacral vesicles appear to have been seen 

 by Monro (V'ergleichung des Baues und der Phy- 

 siol, der Fische, 1787, p. 91, Taf. XXXIII. fig. 

 13-15 ; or Cyclopaedia of Anat. and Phvsiol. 11. 

 p. 35, fig. 14). Krohn {Muller's Arch. "lS41, p. 

 5) has accurately described them. It is affirmed 

 that the ambulacra of Echinus can be filled with 

 water through an opening of the suclcer at their 



extremity, and that it is discharged from the aquif- 

 erous system through ten openings between the 

 teeth ; see Tiedemann, loc. cit. p. 81 ; Falentin, 

 Monogr. &c. p. 84, or Repertor. f. Anat. 1843, p. 

 237 ; and Monro, loc. cit. p. 92. 



a Tiedemann, loc. cit. Taf. II. fig. 4, e. e. fig. 

 6, m., and Delle Chiaje, loc. cit. Tav. YIII. IX. 



!<• Tiedemann, loc. cit. Taf. II. fig. 4, a. a. fig. 

 6, g. ; Delle Chiaje, loc. cit. Tav. IX. fig. 6, f. 

 (Hoiothuria tubnlosa). 



'I The position of the tentacular vesicle seems 

 exactly adapted to enable them to force, during 

 their contraction, their water into the tentacles, 

 thus causing the prominence and development of 

 these last. I am yet uncertain if they are not 

 aided by the vesicles of Poli. ^^'ith some Holo- 

 thurinae, as with Cladolabes spinosus (Atlas 

 zool. du Voyage de I'Astrolabe. PI. VII. fig. 3, f.), 

 and with Pentacta doliolum according to my own 

 observations, the aquiferous ring has only one ve- 

 sicular appendage, and it would be questionable 

 whether this is analogous to a tentacular vesicle, 

 or to one of PoU. 



Thyone and Cuvieria have, according to Ko- 

 ren (loc. cit. p. 20, 36, fig. 2, 11), only a single 

 ■large, vesiculiform appendage upon their aqueous 

 ring. 



12 See Delle Chiaje, loc. cit. Tav. IX. fig. 6 

 {Holothuria tiibnlosa) ; but here also the aiiuife- 

 rous is confounded with the sanguineous system. 



'■i In Chirodota Doreijana, and fiisca, theso 

 hollow tentacular vesicles are very apparent ; see 

 Atlas zool. du ^■oyage, &c., loc. cit. PI. VII. fig. 16, 

 PI. VIII. fig. 3. 



H quatrefages, loc. cit. p. 58, PI. IV. fig. 1, 

 PI. V. fig. 5. 



15 That the tentacular membrane of the Sipun- 

 culidae has the function of a branchia, is indicated 



