206 $ 191. 
THE ACEPHALA. 
connected'with ‘he walls of the intestine, almost inseparably, and opens 
into it through numerous canals. ; 
With the Tunicata, its structure is quite simple, being composed of 
small, single, or ramified glandular follicles, thickly-set together and cover- 
ing a large portion of the stomach and intestine. 
With the Brachiopoda, there are groups of green follicles removed from 
the digestive canal but communicating with it by excretory canals. 
With the Lamellibranchia, this organ is voluminous and composed of 
lobes which occupy the upper part of the abdominal cavity. These lobes 
are made up of distinct Acini formed of brownish-yellow hepatic cells. 
The biliary ducts which open into the stomach or the anterior part of the 
intestine, are always few in number. 
CHAPTER VI. 
CIRCULATORY SYSTEM. 
§ 191. 
This system with the Acephala, as well as that of the Mollusca in gen- 
eral, is of a higher grade than that of the Zoophytes and Worms, in hav- 
ing the movement of the blood due always to a contractile central organ, 
or Heart. 
ers it is so developed as to contain both auricles and ventricles. 
This heart is, it is true, very simple in some, but then with oth- 
It receives 
the blood from the respiratory organs and distributes it over the body, and 
is therefore an Aortic heart. 
As to the blood-vessels themselves, the hith- 
erto received opinions have been of late quite seriously objected to; and it 
appears very probable that all these animals have only arteries and veins, 
of Brachi- 
glandular apy of the i 
opoda are hepatic organs.* 
2 The intestinal nucleus of Salpa owes its yellow- 
ish-brown color to these hepatic organs. But 
with Salpa democratica, and caerulescens, it is 
of a beautiful blue color. 
Sapa pinnata, whose straight intestine has al- 
ready been mentioned, is distinguished also by its 
liver which is separated from and runs parallel 
with the intestine ; see Cuvier, and Meyen, loc. cit. 
This last-mentioned author affirms that he has seen 
with this species a kind of green gall-bladder (loc. 
cit. p. 389, Tab. XX VII. fig. 19, m.) ; but probably 
he confounded the stomach of the animal with its 
liver. For the intimate structure of the glandular 
layer upon the intestine of Salpa cordiformis, 
see Eschricht, Over Salperne, p. 27, Tab. III. fig. 
20. With the Ascidiae, the liver is a simple gland- 
ular layer upon the stomach and intestine in the 
various species of Phallusia and Diazona; while 
with Cynthia, it is isolated near the pylorus, and 
composed of large follicles; see Savigny, loc. cit. 
Pl. XII. fig. 14 (Diazona). 
8 With T'erebratula, there are two groups of 
follicles opening into the stomach; with Orbicula,, 
these are replaced by a mass of long hepatic ones ; 
and with Lingula, by three principal glandular 
masses, opening at different points into the intesti- 
nal canal; see Owen, Cuvier, and Vogt, loc. cit. 
4 Poli (loc. cit. Tab. XI. XV. XVI.) has given a 
good representation of some hepatic lobes with their 
interanastomosing ducts of severa] species. See 
also Bojanus’ figures of the liver and its ducts 
of Anodonta (Isis, loc. cit. p. 757, Taf. IX.). 
As to the intimate structure of this organ, I have 
found with Cyclas cornea, lacustris, and rivi~ 
cola, Unio pictorum, and Tichogonia polymor- 
pha, short, cylindrical, transparent filaments, a lit- 
tle flexed, but projecting stify from the base of the 
follicles into their cavity. I am yet ignorant as to 
their function, but have in vain sought for it, with 
Unio batava, tumida, Anodonta anatina, cyg- 
nea, Mya arenaria, Cardium edule, and Mytilus 
edulis. . 
For the intimate structure of the liver of Lamelli- 
branchia, see H. Meckel (Miller’s Arch. 1846, 
p. 9, Taf. I.) and Karsten (Nov. Act. Nat, Cur. 
XXI. p. 302, Tab. XX.). 
*(§ 190, note 1.] Frey and Leuckart declare the presence of salivary glands with Teredo nava-~ 
dis ; see loc. cit. — Ep. 
