§ 92. THE ECHINODERMATA, 98 
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 pyriform appendages, and 
its main trunks pass along the internal wall of the shell. The ambulaeral 
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 Poliana).°” 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 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 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 five angles of the aqueous vascular ring ; see 
Delle Chiaje, loc. cit. II. p. 296 ; Tiedemann, loc. 
cit. p. 62, Taf. VILL. ; 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, 
and which resemble in some regpects 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, 145 Tiedemann, 
loc. cit. Taf. VIII. 0. 0., or Wagner, Icon. zoot. 
Tab. XXXII. fig. 2, m. 
4 Ophidiaster, Asteracanthion, Luidia ; 
Miller 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 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 sanguineous vessels of the intestinal canal. 
7 Faientin, Monogr. &c. Pl. CXXXIV.— 
OXxx 
8 The anal vessels ramifying upon the flat- 
tened ambulacra! vesicles appear to have been seen 
by Monro (Vergleichung des Baues und der Phy- 
siol. der Fische, 1787, p. 91, Taf. XX XIII. fig. 
18-15; or Cyclopedia of Anat. and Physiol. II. 
p. 35, fig. 14). Krohn (Muller’s Arch. 1841, p. 
5) 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 
see 
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 Repertor. f. ‘Anat. 1843, p. 
237; and Monro, ‘oc. ‘cit. p. 92. 
9 Tiedemann, loc. cit. Taf. Il. fig. 4, e. e. fig. 
6, m., and Delle Chiaje, loc. cit. Tay. VIII. IX. 
10 Tiedemann, loc. cit. Taf. IL. fig. 4, a. a. fig. 
6, g.5 Delle Chiaje, loc. cit. Tay. LX. fig. 6, f. 
(Holothuria tubulosa). 
1! 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’Astrolabe, Pl. VIL. fig. 3, f.), 
and with Pentacta doliolum according to my own 
observations, the aquiferous ring has only one ye- 
sicular appendage, and it would be questionable 
whether this is analogous to a ventaculas vesicle, 
or to one of Poli. 
Thyone and Cuvieria have, according to Ko- 
ren (loc. cit. p. 20, 36, fig. 2, 11), only # single 
large, vesiculiform appendage upon their aqueous 
ring. 
12 See Delle Chiaje, loc. cit. Tav. IX. fig. 6 
(Holothuria tubulosa) ; but here also the aquife- 
rous is confounded with the sanguineous system. 
13 In Chirodota Doreyana, and fusca, these 
hollow tentacular vesicles are very apparent ; see 
Atlas zool. du Voyage, &c., loc. cit. Pl. VIL fig. 16, 
Pl. VIII. fig. 3. 
i4 Quatrefages, loc. cit. p. 58, Pl. IV. fig. 1, 
Pl. V. fig. 5 
15 That the tentacular membrane of the Sipun- 
culidae has the function of a branchia, is indicated 
