^ 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 pjriform appendages,'-' and 

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

 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 PolianajJ'^''^ 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 

 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 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 Sipunculoidea, 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 Sipuneulidae. With 

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

 of an aquiferous system. '^^' 



last species they are only slightly developed ; in extremity, and that it is discharged from the aquif- 



Astropecten aurantiacus there nvethreeUi seven erous system through ten openings between the 



vesicles, opening by a common duct into each of teeth ; see Tiedemann, loc. cit. p. 81 ; Valentin, 



the five angles of the aqueous vascular ring ; see Monogr. &c. p. 84, or Repertor. f. jVjiat. 1843, p. 



Delle Chiaje, loc. cit. II. p. 296 ; Tiedemann, loc. 237 ; and Monro, loc. cit. p. 92. 



cit. p. 52, Taf. VIII. ; Konrad, loc. cit. fig. 3 ; and 9 Tiedemann, loc. cit. Taf. H. fig. 4, e. e. fig. 



Meckel, Syst. d. vergleich. Anat. V. p. 32. Here 6, m., andJOci/e Chiaje, loc. cit. Tav. Vin. IX. 



should be mentioned also the glandular corpuscles 10 Tiedemann, loc. cit. Taf. II. fig. 4, a. a. fig. 



which are attached to the aqueous vascular ring, 6, g. ; Delle Chiaje, loc. cit. Tav. IX. fig. 6, f. 



and which resemble in some respects the glandular {Holothuria tubulosa). 



organs of the vascular sanguineous rings of Echi- n The position of the tentacular vesicle seems 



nus, pomted out by Valentin; see Delle Chiaje, exactly adapted to enable them to force, during 



loc. cit. n. Tav. XXI. fig. 12, 14 ; Tiedemann, their contraction, then- water into the tentacles, 



loc. cit. Taf. VIII. o. o., or Wagner, Icon. zoot. thus causing the prominence and development of 



Tab. XXXII. fig. 2, m. these last. X am yet uncertain if they are not 



4 Ophidiaster, Asteracanthion, Luidia ; see aided by the vesicles of PoU. With some Holo- 

 Miiller and Troschel, loc. cit. Taf. XI. fig. 4. thurinae, as with Cladolabes spinosus (Atlas 



5 A.ttropecten ; see Konrad, loc. cit. fig. 4. I zool. du Voyage de 1' Astrolabe. PI. VII. fig. 3, f.), 

 am not yet settled upon the question whether the and with Pentacta doliolum according to my own 

 aquiferous system of the Asteroidae is filled by the observations, the aquiferous ring has only one ve- 

 extremity of the ambulacra, or by the oral ring. I sicular appendage, and it would be questionable 

 have not been able to convince myself of the pres- whether this is analogous to a tentacular vesicle, 

 ence of an opening at the extremity of these first, or to one of Poll. 



6 Delle Chiaje (loc. cit. Tav. XXVI.) has given Thyone and Cuvieria have, according to Ko- 

 very detailed figures of the aquiferous system of ren (loc. cit. p. 20, 36, fig. 2, 11), only a smgle 

 Echinus and Spatangus ; but he has confounded it large, vesiculiform appendage upon their aqueous 

 with the sanguineous vessels of the intestinal canal, ring. 



7 Valentin, Monogr. &c. PL CXXXIV.— 1:^ See Delle Chiaje, loc. cit. Tav. IX. fig. 6 

 CXXXVI. (Holothuria tubulosa) ; but here also the aquife- 



8 The branchial vessels ramifying upon the flat- rous is confounded with the sanguineous system, 

 tened ambulacral vesicles appear to have been seen 13 in Chirodota Doreijana, and fusca, these 

 by Monro (Vergleichung des Baues und der Phy- hollow tentacular vesicles are very apparent ; see 

 siol. der Fische, 1787, p. 91, Taf. XXXHI. fig. Atlas zool. du Voyage, &c., loc. cit. PI. VII. fig. 16, 

 13-15 ; or Cyclopsedia of Anat. and Physiol. II. PL Vm. fig. 3. 



p. 35, fig. 14). Krohn (Mailer's Arch. 1841, p. H Quatrefages, loc. cit. p. 58, PI. IV. fig. 1, 



5) has accurately described them. It is aflirmed PL V. fig. 5. 



that the ambulacra of Echinus can be filled with 15 That the tentacular membrane of the Sipun- 



water through an opening of the sucker at their culidae has the function of a branchia, is indicated 



