374 THE OCEAN WORLD. 



flat triangular lips, by means of which the animal introduces its food 

 into the stomachal cavity. 



A very short gullet is attached to the mouth, which leads to a 

 pear-shaped stomach. After this stomach comes a slender sinuous 

 intestine, which, leading obliquely towards the interior, descends a 

 little, then re-ascends, passes behind the stomachal cavity, nearly on 

 a level with the mouth, crossing its first path in order to reach the 

 posterior face of the adductor muscle, in the centre of which it 

 terminates with a free opening. The stomach and intestines are 

 surrounded on all sides by the liver, which alone constitutes a notable 

 portion of the total mass of the organs. This liver is of a blackish 

 colour, pervaded with a deep yellow liquid, which is the bile. Thus, 

 the stomach and intestines of the oyster are surrounded by the liver ; 

 the mouth is connected with the stomach, and the intestinal canal 

 has an opening of its own. 



The heart of the oyster is placed under the liver, and is sur- 

 rounded closely by the terminal part of the intestines. It is com- 

 posed, like the same organ in the superior animals, of two distinct 

 cavities, an auricle and ventricle. From the ventricle issues a vessel, 

 Avhich is divided into three distinct canals. One of these carries the 

 blood towards the mouth and labial tentacles ; another carries it 

 towards the Hver ; the last distributes the nourishing fluid to the rest 

 of the body. The blood of the oyster is limpid and colourless ; it 

 passes successively from the auricle of the heart, where it is vivified, 

 int-o the ventricle, and from this last cavity into the great vessel of 

 which we spoke, which distributes it throughout the interior of the 

 animal. 



The oyster thus possesses a true circulation ; not that double 

 system which characterises the mammals, and which includes arterial 

 and pulmonary action, but a simple circulation, as it exists in fishes 

 and many other animals. It breathes also under the water, after the 

 manner of fishes, being, like the fish, provided with organs called 

 gills or branchice, whose function is to separate the oxygen dissolved 

 in the water from its other ingredients ; these branchiae, which are 

 placed between the mantle folds, consist of a double series of very 

 delicate canals, placed close together, not unlike the teeth of a fine 

 comb. 



Having no head, the oyster can have no brain ; the nerves 

 originate near the mouth, where a great ganglion is visible, whence 

 issues a pair of nerves which distribute themselves in the regions of 

 the stomach and liver, terminating in a second ganglion, situated 

 behind the liver. The first nervous branch distributes its sensibility 



