912 SUPPLEMENT 
times double when the gills are symmetrical and lateral, as 
in the brachiocephala and conchiferous acephala, and of a 
ventricle. 
The auricle, of a very variable form, ordinarily oval, some- 
times triangular, has its parietes very slender. We may ob- 
serve, however, at the interior some muscular cords which 
traverse it. It does not appear that there is any valvule at 
the entrance of the branchial or pulmonary vein into this 
auricle. 
Its communication with the ventricle is made by a sort of 
pedicle or contraction, often pretty long, as in the calmars, for 
example, and by means of a narrow orifice usually transverse, 
situated between two folds of the internal face of the ventricle, 
but without valvules, properly so called, something in the way 
that the small intestine opens into the ccecum in the human 
species. 
The ventricle, in general much thicker, is also of a form and 
direction very variable; its parietes are always thicker than 
those of the auricle, and we can very well distinguish the 
transverse muscular bundles which form it, between two of 
which is the auriculo-ventricular orifice. 
It is from its point, or from one of the extremities of its 
greatest diameter, that the arterial or centrifugal system pro- 
ceeds, most usually by a single trunk, but sometimes also by 
two, as may be well observed in the calmars. 
The arteries of the mollusca have evidently their parietes 
more thick and more resistant than the veins. They possess 
great elasticity; and in the largest of these animals, they 
appear of a gelatinous tissue, without any trace of fibres. 
Their distribution is too variable to speak generally con- 
cerning it; nevertheless, most commonly there are two prin- 
cipal trunks, one anterior and the other posterior. ‘The first 
furnishes branches to the head and to its different parts, to 
the esophagus, and even to the anterior organs of generation ; 
a 
