166 ANATOMY OF THE LAMELLIBRANCHIATA. 



leaves its extremity, as in some Tellium, &c, or diverges 

 from its side at a greater or less distance from the end, as in 

 Cardium, Solen vagina, &c. The parietes of the duodenum 

 are glandular. The remainder of the canal has many veins 

 originating from it, which perhaps act the part also of lacteals. 

 The extremity of the duodenum is always near the pedal pore 

 and perhaps the vitellus of the embryo so enters. The intes- 

 tine varies much in length. As shewn by Poli, those species 

 which are fixed have it shortest. In Anomia it is not an inch 

 long, and makes no turn ; it has a rounded projecting process 

 in its whole length. A similar projection is seen in other 

 genera. The convolutions of the intestine interwoven with 

 the liver and ovaries, are generally contained in great part in 

 the foot. In the Monomyaria, in the Mytilus, Pinna, &c, 

 it makes only two or three turns, the last often surrounding 

 the stomach. In the fresh water species it is longer by a 

 turn or two ; longer still in Pholas, Mya, Venerupis, Tellina, 

 &c. ; but longest of all in Cardium, Donax, Venus, Mactra, 

 and some other genera, where it is sometimes ten or twelve 

 times the length of the animal. The intestine, having made 

 its convolutions, is directed towards the heart, through the 

 ventricle of which it commonly passes, and ends on the pos- 

 terior muscle by an opening, which, in some species, has a 

 divided margin. This anus is situated between the lobes of 

 the mantle, and opens into the superior of the two tubes, 

 when they exist. In the oyster the ventricle is not perfo- 

 rated by the intestine, the heart being in a different situation. 

 In the Anomia the heart lies upon it. When there are two 

 ventricles, as in Area, Lima, and certain Pectunculi, the in- 

 testine passes between them. In the Unio it has been de- 

 scribed that the intestine makes its escape from the cavity of 

 the heart to re-enter it again ; such a description is not taken 

 from the normal disposition of the animal. The curious cir- 

 cumstance of the perforation of the ventricle by the intestinal 

 tube appears to be a result merely of the disposition of the 

 parts. 



The liver, in all the Lamellibranchiata, surrounds the ca- 

 vity of the stomach, into which its secretion of greenish bile 

 is poured by one or more ducts. It has no vena porta going 

 to it, but its arteries, and hepatic veins are large. Its situa- 

 tion is at the anterior and superior part of the animal, and it 

 is composed of a multitude of oval granules, differing in size 

 in different species, opening into the termination of the ra- 

 muscules of the duct. 



