OYSTERS AND OYSTER-CULTURE. 
451 
gills to breathe by, muscles to close his valves, reproductive 
glands and nerves. First, of his digestive system : there can 
hardly be said to be a gullet ; the mouth which is placed at the 
bottom of the mantle cavity, and which is provided with a 
pair of fleshy lips, opens almost directly into a large stomach 
which is perforated by the canals, bringing bile from the liver. 
To the other end of the stomachal sac is attached the intes- 
tine ; this is longer in the oyster than in most bivalves, and is 
very much twisted and coiled, in its passage to the anus, which 
lies upon the back of the muscle that closes the valve, and is 
placed upon a projection which points towards the smaller 
shell. The liver is a large and important gland, buried in the 
substance of the animal, and of a deep brown colour. It 
consists of numerous lobes or folds, which in their turn 
contain smaller cavities, within which the true hepatic cells 
may be seen.* * * § The process of digestion is carried on as much 
in the intestine as in the stomach, and consists in the solution 
and absorption of the green vegetable matter ( Navicula ) upon 
which the animal feeds. The heart — unlike that of most of 
the oyster’s kindred — is not perforated by the intestine ; so that, 
as an amusing writer observes, “ the way to his heart is not 
through his stomach.” It is situate at the hinder extremity 
of the creature’s back, and is composed of three cavities, two 
of which receive the blood which has been purified in the gills, 
and the third of which pumps the vital fluid through the 
arteries. The circulation, however, is not a perfect one, for 
there are no vessels between the arteries and the veins, and 
the blood which escapes from the former traverses the different 
spaces ( lacunae ) of the body before it enters the latter. The 
nutritious fluid itself is colourless, but contains several of 
those ee coarse granules ” which were first pointed out by 
Mr. Wharton Jones, f These spaces form a beautiful network, 
which, however, must not be confounded with another series 
of cavities, supposed by some to be connected with what 
is called an “ aquiferous system.” J The gills or branchiae 
have been observed by every one : they are those delicate 
fringes which are seen within the beard when the oyster is 
opened. These, which are four in number, are composed of 
folds of the membranous mantle containing blood vessels 
abundantly, and covered on their outer surface with thousands 
of delicate vibratile microscopic filaments called cilia. Accord- 
ing to Williams’s researches, § these gill-plates are chiefly 
* See Meckel’s memoir in Miiller’s “ Archives fair Anatomie.” 1846, p. 9. 
t “ Philosophical Transactions,” 1846. 
X Consult Milne Edwards’s Memoir in Comptes Bendus, XX., p. 271. 
§ “Reports of British Association” for 1851, p. 82 
