90 THE ECHINODERMATA. $ 88. 
In the Echinidae, the heart is long,“) and attached to the oesophagus. 
In Echinus, it has several saccular enlargements, and internally has a 
cavernous aspect, due to numerous irregularly arranged septa. At each 
of its extremities there are two vascular rings. The two below are situated 
on the top of the lantern and surround the cesophagus, while the two- 
above surround the anus; all belong probably to the arterial and venous 
systems. One of these last sends off five branches to the genital organs, 
while the other receives one of the two trunks which pass along the whole 
length of the intestinal canal. Two longitudinal vessels, which send off 
branches right and left, pass between each of the five pairs of ambulacral 
organs. These are, probably, a branchial artery and vein.” 
In the Holothurinae, the vascular system, which is without a heart, is 
very distinct. An aortal trunk arises from the vascular ring, which sur- 
rounds the wsophagus, and ramifies upon the intestine and the genital 
organs. By a reunion of these ramifications, a second trunk like a vena 
cava, is formed. This divides into two arteries, which ramify upon the 
branchiae, and from which arise two branchial veins, which return to the 
aorta, © 
With the Sipunculidae, and Hchiuridae, there is a main vascular 
trunk, which, after sending off laterally small branches, passes along the 
ventral median line, above the digestive canal.” 
its relations with the rest of the vascular system. 
Moreover, he has taken for an isolated, special 
sanguineous system belonging to the ambulacra, 
the aquiferous system, which communicates directly 
with the ambulacra, and which forms a third ring, 
situated between the two sanguineous ones of the 
mouth. 
Volkmann’s description (Isis 1837, p. 518) is 
wholly different. According to him, the vascular 
trunks of the superficial ring, and which are 
located in the furrows of the arms of Asteracan- 
thion violaceus, send off laterally ambulacral 
branches; the oral ring, situated more deeply, 
sends off branches, which, passing through the 
cavity of the body, go to the rays and ambulacra 
and freely communicate with the cavity of 
these last. This same ring has also an anas- 
tomotic connection with that of the back. Accord- 
ing to this, the circulation occurs, he thinks, in the 
following manner: The heart sends the blood into 
the superficial oral ring; thence it passes by the 
vessels in the furrows of the arms into the cavity 
of the ambulacra; these last, acting as venous 
hearts, send it, by the vessels in the interior of the 
rays, to the second oral ring, from which it passes 
e the third and dorsal ring, and thence to the 
eart, =~ 
It is ewident that Volkmann has taken a part 
of the aquiferous system for that of the sanguineous 
one ; and it is probable that he did not observe the 
second oral ring. No correct idea can be formed 
of the distribution of the arteries and veins of the 
Asteroidae, or of their vascular system in general, 
except by carefully separating it from the aquifer- 
ous system, and considering the fact that the blood- 
vessels do not open into the ambulacral vesicles, 
but probably are spread as a capillary net-work 
upon their walls. 
4The heart of Echinus, which is accurately 
described by Valentin (Monogr. &c. p. 92, Pl. 
*[§ 88, note 6.] See, for the vasoular system 
of the Holothurioidea, Miller (Arch. 1850, p. 
229), who has carefully studied it with the larger 
- Synaptinae. He confirms T'iedemann’s observa- 
VIIL.), is attached to the 
mesentery. ‘ 
5 These details are supported by Valentin (loc. 
cit. p. 93), who has already added much to the 
labors of Tiedemann and Delle Chiaje upon the 
sanguineous system of Echinus, although, like his 
predecessors, he has been deceived as to its con- 
nections. 
The received opinions upon the circulation of 
these Echinoderms are, therefore, hypothetical. The 
nature of the five glandular organs, which Val- 
entin has seen communicate with one of the two 
vascular rings situated upon the lantern, is very 
problematical (Monogr. &c. p. 95, Pl. VII. fig. 
119, i. 120). 
6 See Tiedemann, loc. cit. p. 15. The sanguine- 
ous system of Synapta Duvernaea, as described 
by Quatrefages (loc. cit. p. 58), corresponds, 
properly, to the aquiferous system of Holothuria, 
which Tiedemann also has taken for a special 
sanguineous system of the skin and ambulacra. 
Hereafter we shall notice further both of these sys- 
tems.* * 
7 For the sanguineous vascular system of Sipun- 
culus, and Echiurus, see Grube and Krohn (Mi- 
ler’s Arch. 1837, p. 248; 1839, p. 350), also 
Forbes and Goodsir (Froriep’s neue Not. No. 
392, loc. cit.). The vascular trunk embraces there 
the nerve so closely, that care is necessary not to. 
overlook one, or confound both together. 
Quatrefages has found in the anterior part of 
the body of Echiurus Gaertneri three heart- 
shaped swellings of the blood system, namely, a 
ventral heart upon the ventral vessel, a dorsal 
heart upon the dorsal vessel, and a mesenteric 
heart situated beneath the digestive tube. This 
last communicates with the ventral heart by a 
flexuous vascular canal, and with the dorsal vessel 
by a small vascular ring ; see Ann. d. Sc. Nat. loc. 
cit. p. 324, Pl. VI. fig. 4. 
phagus by a kind of 
tion above quoted as to the general distribution of 
the vessels, and especially as to the presence of a 
splanchnic system, which, as is well known, Qua 
trefages has supposed to be wanting. — Ep. 
