$ 192. THE ACEPHALA. 20T 
which are connected by no capillary net-work except that situated in the 
respiratory organs. The blood leaving the open ends of the arteries passes 
into the interstices (Lacunae) of the parenchyma of the body; thence it is 
taken up by the open mouths of the venous radicles.® 
The Blood is colorless and contains many pale, granular globules, which 
ate indistinctly nucleated. 
§ 192. 
With Sapa, the circulatory system is composed of two main trunks, one 
‘upon the dorsal, and the other upon the ventral median line. At the ante- 
rior extremity of the body these trunks connect by two arcuate vessels ; 
and at the posterior extremity by a single slightly-dilated canal situated | 
directly in front of the intestinal nucleus. ‘This last-mentioned canal is 
‘divided into several chambers by two or three constrictions, and, from its 
rhythmical contractions, may be regarded as a heart.” It is surrounded 
‘with a delicate pericardium,” and by its pulsations the blood is thrown across 
the walls of: the body in different ways, thus forming extra-vascular cur- 
rents. But it will here be observed that the heart, thus forcing the blood 
-alternately in one direction and then in another, will regularly change the 
arterial into a venous current, and vice versa. 
With the Ascidiae, this system is equally feebly developed. The blood 
passes for the most part out of the vessels into the lacunae which often con- 
sist of ramified canals resembling vessels. The Heart is always present, 
and is surrounded with a very thin pericardium. It consists of a lon 
-canal, which, at both extremities, passes into a vessel which lies loop-like 
between the vascular sac and the intestine at the lower part of the cavity of 
the body.” Its pulsations quite resemble the peristaltic movements of the 
1 This effusion of the blood into the parenchyma 
of the body and its return into the veins without 
the intervention of capillaries, or in general with- 
out walled canals, has been maintained recently, es- 
specially by Milne Edwards (Observ. et expér. sur 
la circul. chez les Mollusques, Comp. Rend. XX. 
1845, p. 261), and by Valenciennes ‘Nouv. observ. 
sur la constit. de Pappareil de la circul. chez les 
Mollusques, Ibid. p. 750). Their observations 
were not limited to Sa/pa, and the Ascidiae, but 
were extended upon Ostrea, Pinna, Mactra, Ve- 
‘nus, Cardium and Solen. See also Ann. d. Sc. 
Nat. III. 1845, p. 289, 307, or Froriep’s neue Not. 
-Nos. 732, 733, 748. 
Milne Edwards is about to publish an extended 
work on the circulation with the Mollusca. He has 
figured from his beautiful injections the partly la- 
-cunal circulatory system of Pinna ; see Ann. d, Sc. 
Nat. VIII. 1847, p. 77, Pl. IV. 
2 For the blood of Phaliusia, Cynthia, and Ano- 
donta, see Wagner, Zur vergleich. Physiol: d. 
-Blutes Hft. I. p. 20, I. p. 40. The blood-corpuscles 
of the Naiades have always appeared to me of an 
irregular form ; and they run together when placed 
ina watch-glass. This is probably due to the fibrin 
cementing them together. When treated with ace- 
tic acid they become separated again, their contour 
becomes very clear and almost imperceptible, and 
-a hitherto invisible nucleus is seen. 
1 See Cuvier, loc. cit. p. 10, fig. 2,.9, &c. Ac- 
cording to Meyen (loc. cit. p. 375, Pl. XX VIII. fig. 
1, d.) the heart of Sa/pa mucronata has two con- 
Strictions ; and, according to Eschricht, that of 
Salpa cordiformis is divided into four chambers 
loc. cit. p. 26, fig. 8, a). 
2 Meyen - (loc. cit. p. 376) has denied the pres- 
ence of a pericardium with Salpa ; but Cuvier (loc. 
cit. p. 10), Savigny (loc. cit. p. 127), and Delle 
Chiaje (Vescriz. &c. III. p, 43, Tay. LXXVIII.) 
affirm the contrary. 
8 The direction of these blood-cprrents in the 
body of Salpa is satisfactorily shown by the de- 
scriptions and figures of Quoy and Gaimard (loc. 
cit.) and especially of Delle Chiaje (Descriz. &c. 
Sars (Faun. litt. &c. p. 66), has also observe 
with Sa/pa runcinata, that the blood beyond the 
aorta and vena cava, circulates in wall-less pas- 
sages. 
4 This remarkable alteration of the blood-currents 
which is possible only with a valveless heart, has 
been observed and described by different observers 
inaconformable manner. Before the heart chang- 
es the direction of its contractions it remains still 
for a short time, and this.slackens the course of the 
blood-currents in the body a little, before they re~ 
ceive an impulse in the opposite direction; see 
Van Hasselt (Ann. d. Sc, Nat. III. 1824, p. 78). 
Eschscholtz (Muller’s translation of the annual 
report of the Swedish Academy upon the progress of 
Natural History, &c., 1825, p.94), Quoy and Gai- 
mard (loc. cit. p. 559, or Isis. 1836, p. 111), and 
Delle Chiaje (Descriz. &c. III. p. 48). 
5 For the heart and blood-system of the Asci- 
diae, see especially, Milne Edwards (Sur les Asci- 
dies composées loc. cit. p. 4), who has indicated the 
presence of the heart in Phallusia and Clave- 
-lina, as well as in Polyclinum, Botryllus, Di- 
demnum, Pyrosoma, &c. 
