208 THE ACEPHALA. $ 192. 
intestine; and, as with Salpa, the direction of the current is changed so 
alternately that the two terminal vessels serve in rotation as an Aorta and. 
a Vena cava. 
The blood not only traverses the lacunae of the intestinal sac, but also. 
penetrates the walls of the mantle, and even passes into the common sup- 
port of the compound forms. In this last case, it circulates in ramified 
canals, which, as prolongations of the cavity of the body, extend even into 
this portion of the mantle. 
With the Brachiopoda, this system is quite remarkable. The branchial 
afferent veins of the mantle do not open into a single heart, but into two. 
hearts which are situated right and left of the intestinal sac. ; 
These hearts, by pulsation, throw the blood into the intestinal canal, 
which ought therefore to be considered as a common visceral sinus.” 
With the Lamellibranchia, the heart, situated at the posterior extremity 
of the back, is divided, usually into three chambers, and surrounded with 
a large pericardium. Two lateral, triangular, thick-walled auricles receive 
the blood from the branchiae and send it into a simple muscular ventricle: 
which is nearly always traversed by the rectum. Thence the blood passes 
into the body by a posterior and an anterior aorta. Its return into the 
two auricles is prevented by valves.©? The walls of these aortae disappear 
after considerable ramification, and the blood passes into a system of lacu- 
nae which extends through the whole body and forms a net-work of sinuses. 
and anastomosing canals,“ 
6 This change in the direction of the blood-cur- 
rents was first noticed by Lister (Philos. Trans. 
1834, Pt. II. p. 365, or Wiegmann’s Arch. 1835, 
I. p. 309) with Perophora, a new genus of the 
compound Ascidiae; and Milne Edwards has 
since confirmed it with Pyrosoma (Ann. des Sc. 
Nat. XII. 1839, p. 375), and several other Ascidiae 
hoth simple and compound ; see his Observ. sur 
les Ascidies simples et composées, p. 7. 
These inter-alternating peristaltic and anti-peris- 
taltic motions show that the heart of the Ascidiae 
is valveless. It is therefore surprising that Dedle 
Chiaje has described it with valves; but this is 
not the only point in which he differs from other 
observers on this subject, for he describes the heart 
of the Ascidiae as bifurcated into two auricles ; see 
his Mem. &e. loc. cit. III. p. 198, Tav. XLVI. fig. 
18, ab. (Cynthia papillata), and Descriz. &c. III. 
p. 29, Tav. LXXXII. fig. 11, 12 (Phallusia in- 
testinalis). 
7 This circulation of the blood in the common 
Ascidian-stock has been observed by Lister (loc. 
cit.). Milne Edwards has seen also the ascending 
and descending currents in the ramified and coecal 
prol ions of the peri 1 sac, in Botryllus, 
Diazona, Didemnum, and Polyclinum ; see Sa~ 
vigny, Mém. loc. cit. p. 47 ; Delle Chiaje, Descriz. 
&c. IIL. p. 34, Tav. LXXXIIL. fig. 13, 15; and 
Milne Edwards, Sur les Ascidies, loc. cit. p. 41, 
Pl. VIL fig. 1,1. 1s. This last-mentioned author 
has also observed that, with Clavelina (Ibid, p. 
9. PI. IT.), these canals terminate in caeca which 
communicate with the cavity of the body, and are 
extended into digitiform prolongations upon the ex- 
tremity of the peritoneal sac, and herein the blood 
moves alternately up and down. The ramified ca- 
nals which abundantly traverse the mantle of Phal- 
lusia, are, according to authors, real blood-vessels 5 
see Cuvier, loc. cit. p. 16, Pl. III. fig. 1; Savigny, 
loc. cit. p. 102, Pl. IX. fig. 1, B., and Delle Chiaje, 
* [§ 192, note 10.] See also Deshayes, loc. cit, 
Sages, loc. cit. p. 47, Pl. I. fig. 7 (Teredo).— Ep. 
The venous blood is received into special 
Descriz. &c. III. p. 33, Tav. LXXXIV. fig. 2. 
According to Kélliker (Ueber das Vorkommen der- 
Holzfaser im Thierreich. loc. cit.), these multira- 
mose vessels which come directly from the heart. 
and whose extremities are penicillated, appear to be- 
inuous directly b th the skin with other’ 
vessels returning by the course of these arteries. 
8 See Cuvier, Owen, and Vogt, loc..cit. 
9 Owen was the first to notice this analogy of 
the circulation of the Brachiopoda with the extra 
vascular one of other Acephala ; see his Lettre sur- 
) Appareil de Ja cir ion chez les Mollusques de la. 
Classe des Brachiopodes (Ann. d. Sc. Nat. III. 1845, 
p. 315, Pl. IV., or Froriep’s neue Not. No. 793). 
10 For the arrangement of this central part of the- 
circulatory system, see Poli, loc. cit. Tab. IX. fig. 
12 (Unio) ; Tab. XIII. fig. 5 (Solen) ; Tab. XXII. 
fig. 10 (Spondylus) ; Tab. XXVII. fig. 8, 12 (Pec— 
ten) ; Tab. XXIX. fig. 7,8 (Ostrea) ; Tab. XX XT. 
fig. 8, 9 (Mytilus), and Tab. XXXVIII. XX XIX. 
(Pinna). Also Bojanus, in the Isis, 1819, , 42, 
Taf. I. I. (Anodonta) ; Treviranus, Beobachi aus 
d. Zoot. u. Physiol. p. 44, fig. 67 69 (Mytilus and 
Anodonta) ; and Garner, Trans. of the Zool. soc. 
IL. p. 90, Pl. XIX. fig. 4 (Pecten). 
An arrangement quite different from this type is- 
found with Arca, whose two auricles are attached 
to the two widely-separated ventricles, and send 
out on each side an anterior and posterior aorta, 
which meet and join upon the dorsal median line ; 
see Poli, loc. cit. Taf. XXV. fig. 2, 3.* 
U1 This system of lacunae forms, especially in the 
mantle, a beautiful net-work of delicate canals- 
which, with the Naiades, are visible to the naked. 
eye. It should not, however, be confounded with 
another net-work more difficult to be seen, and 
which probably constitutes a system of aquiferous. 
canals, which is easily seen in the mantle, foot and 
other parts of the body by inflation. Delle Chi-- 
aje has called it Rete lymphatico-vasculosum, 
» p. 63, 64, &c., Pl. VII. fig. 1, 2,3, and Quatre~ 
