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composed of blood-vessels bent upon themselves, and arranged 
in parallel series ; moreover, the cilia are so disposed as to 
create currents which set in the direction in which the blood 
itself flows. The gills being constantly exposed to the freshly 
oxygenated water, allow the blood to be purified by exposure, 
and then returned to the heart, to be propelled to the various 
organs which require it. The oyster has one good muscle, 
and only one ; it is that which closes the two valves, and 
which is so ruthlessly severed by the knife in opening the 
shell. It is a solid mass of fibres, firmly attached to the inner 
surface of both valves, and situated at about the centre 
of each, which during contraction it approximates to its 
fellow. The nervous system is by no means so unsymmetrical 
as some anatomists would lead us to suppose. There are three 
pairs of nervous centres which are connected by true nerves, 
and the latter send branches over the body. The first pair is 
placed near the mouth, one lying on each side of this organ, 
and being united to its fellow by nervous chords of extreme 
tenuity ; the second is situate behind, close to the gills ; and 
the third, which is feebly developed in our bivalve, is placed 
near the labial mass.* * * § That portion of the nervous apparatus 
which is located near the animal’s mouth, may fairly be re- 
garded as constituting a species of brain. 
A great deal of controversy has taken place regarding the 
connection of the two reproductive organs in this animal, f 
Some naturalists contend that the oyster is hermaphrodite, 
others, that in it the sexes are distinct. J We are inclined to 
adopt the latter opinion, of which we shall have more to say 
further on. Can the oyster see? This question has been 
answered in the affirmative by Will,§ who states that there 
are as many as thirty distinct eyes projecting from the border 
of the mantle ; but Siebold denies that such is the case, and 
regards the so-called eyes as simple excrescences, devoid of 
optical powers. So the question rests. There can, how- 
ever, be little doubt that these molluscs are sensitive to light. 
Having said so much about anatomical characters, we may 
now turn to other matters. The average age of the oyster, 
* Brandt’s “ Medical Zoology,” vol. ii., and Garner, in the “ Linnseaii 
Transactions ” for 1837, p. 485. 
t Ooste, “Voyage d’exploration sur le Littoral de la France.” 1861, 
p. 104. Kemmerer, “ Oyster Cultivation in the Island of Ke,” translated by 
Mr. T. Ashworth, 1864. Lowe, “Journal of Society of Arts,” May 20, 
1864. 
X Quatrefages, Comptes Renclus, t. 28, p. 292. Von Siebold, “ Ver- 
gleichenden Anatomie,” article “ Acephala” 
§ In “ Frorieps Neue Notizen ” fur 1844, No. 622. 
