20G THE ACEPHALA. § 191. 



connected with the 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 

 arc 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 Aeephala, 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. This heart is, it is true, very simple in some, but then with oth- 

 ers it is so developed as to contain both auricles and ventricles. 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, 



glandular appendages of the intestine of Brachi- follicles opening into the stomach ; with Orbicula, 



opoda are hepatic organs.* these are replaced by a mass of long hepatic ones ; 



2 The intestinal nucleus of Salpa owes its yellow- and with Lingula, by three principal glandular 

 ish-brown color to these hepatic organs. But masses, opening at diSVrent points into the intesti- 

 with Salpa dcmocratica, and caerulescens, it is nal canal ; see Owen, Cuvier, and f'ogt, loc. cit. 

 of a beautiful blue color. 4 Poli (loc. cit. Tab. XI. XV. XVI.) has given a 



Sa//>a pinnata, whose straight intestine has al- good representation of some hepatic lobes with their 



ready been mentioned, is distinguished also by its interanastomosing ducts of several species. See 



liver which is separated from and runs i^arallel also Bojanus' figures of the liver and its ducts 



with the intestine ; see Cuuj'er, and Jlfeyen, loc. cit. of Anodonta (Isis, loc. cit. p. 157, Taf. IX.). 



This last-mentioned author affirms that he has seen As to the intimate structure of this organ, I have 



with this species a kind of green gall-bladder (loc. found with Cyclas cornea, lacustris, and rivi- 



cit. p. 389, Tab. XXVII. fig. 19, m.) ; but probably cola, Unio pictorum, and Tichogonia polymor- 



he confounded the stomach of the animal with its pha, short, cylindrical, transparent filaments, a lit- 



liver. For the intimate structure of the glandular tie flexed, but projecting stillly from the base of the 



layer upon the intestine of Salpa cordiforjnis, follicles into their cavity. I am yet ignorant as to 



see Eschricht, Over Salperne, p. 27, Tab. III. fig. their function, but have in vain sought for it, with 



20. With the Ascidiae, the liver is a simple gland- Unio batava, tumida, Anodonta anatina, cyg- 



ular layer upon the stomach and intestine in the nea, Mya arenaria, Cardium edule, and Mytilus 



various species of P/ta//usja and Djazona ; while edulis. 



with Cynthia, it is isolated near the pylorus, and For the intimate structure of the liver of Lamelli- 



composed of large follicles ; see Savigny, loc. cit. branchia, see H. Meckel {Muller\<i Arch. 1846, 



PI. XII. fig. l<i (Diazona). p. 9, Taf. I.) and Karsteu (Nov. Act. Nat. Cur. 



3 With Terebratula, there are two groups of XXI. p. 302, Tab. XX.). 



* [ § 190, note 1.] Frey and Leuckart declare the presence of salivary glands with Teredo nava- 

 lis ; see loc. cit. — Ed. 



