^ 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 Eshinoidea, the oral ring wants the pyriforra appendages,'^' and 

 its main trunks pass along the internal wall of the shell. The ambulacra] 

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

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

 vascular network.® 



The aqueous oral ring of the Holothurinae hag 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 Poliana).^^"^ Opposite the tentacular vesicles, the ring sends oflF 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 

 ofi" 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 oft' 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 Sipunculoi'dea, 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 Poli 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 tive angbs of the aqueous vascular ring ; see 

 Del/e Cltiaje, 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. Here 

 should be mentioned also the glandular corpuscles 

 which are attached to the aqueous vascular ring, 

 an<l which resemble in.some respects the glandular 

 organs of the vascular sanguineous rings of Echi- 

 nus, pointed out by Valentin ; see Delle Chiaje, 

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

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

 Tab. XXXII. fig. 2, m. 



i Ophidiaster, Asteracanthion. Luidia ; see 

 Mailer and Troschel, loc. cit. Taf. XI. fig. 4. 



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

 am not yet settled upon the question whether the 

 aquiferous system of the Asteroidae ig 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 openhig at the extremity of these first. 



•> Del/e Chiaje (loc. cit. Tav. XXVI.) has given 

 very detailed figures of the aquiferous system of 

 Echinus and Spatans;us ; but he has confounded it 

 with the sanguineous vessels of the intestinal canal. 



7 Valentin, Monogr. &c. PI. CXXXIV.— 

 CXXXVI. 



8 The branchial vessels ramifying upon the flat- 

 tened ambulacral vesicles appear to liave been seen 

 by Monro (Vergleichung des Banes und der Phy- 

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

 13-15 ; or Cyclopasdia of Anat. and Physiol. II. 

 p. 35, fig. 14). Krohn {Muller's Arch. "1841, p. 

 6) has accurately described them. It is affirmed 

 that the ambulacra of Echinus can be filled with 

 water through an opening of the sucker 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 ; Valentin, 

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

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



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

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



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

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

 (jlolothuria tubulosa). 



11 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. With some Holo- 

 thurinae, as with Cladolabes spinosus (Atlas 

 zool. du Voyage de l'.\strolabe. 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 Poli. 



Thyone and Cxivieria have, according to Ke- 

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

 large, vesiculiform appendage upon their aqueous 

 ring. 



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

 (Jlolothuria tubulosa) ; but here also the aquife- 

 rous is confounded with the sanguineous system. 



IJ* In Chirodota Doreijana, and fusca, these 

 hollow tentacular vesicles are very apparent ; seo 

 Atlas zool. du Voyage, &c., loc. cit. PI. VII. fig. 16, 

 PI. VIII. fig. 3. 



14 Quatrefages, loc. cit. p. 58, PI. TV. flg. 1, 

 PI. V. fig. 5. 



13 That the tentacular membrane of the Sipun- 

 culidae has the function of a branchia, is indicated 



