ORDER DECAPODA. 
141 
in its progress, and terminating at the anus; The blood which 
has served for the nutrition of these divers organs, and which 
is thus become venous, flows from all parts into two vast 
sinuses, one on each side, above the feet, and formed of 
venous gulfs, united in a longitudinal series, in the manner 
of a chain. It discharges itself into an external vessel of the 
gills, is renewed there, becomes arterial again, passes into an 
internal vessel, and afterwards directs itself towards the heart, 
traversing some canals ( branchio-cardine ) lodged under the 
vault of the flanks. All the canals of the same side are 
united in a wide trunk, have a common opening into the 
lateral and corresponding part of the heart, through one aper- 
ture, whose folds form a double valve, and open to allow the 
blood to proceed from the gills to this viscus, but close to 
shut it out from an opposite direction, or to hinder it from 
passing from the heart to the respiratory organs. Examined 
internally, the heart exhibits a great number of bundles, and 
of muscular fibres intercrossed in various directions, and com- 
posing many small lodges in front of the orifices of the arteries. 
These lodges are so many small auricles, which communi- 
cate together with facility, when it is dilated, but which ap- 
pear to form, for each vessel, when the heart is contracted, 
an equal number of little cells, whose capacity is in relation 
with the quantity of the blood of the vessels which are pro- 
per to them. These vessels open into the interior of the 
heart, by eight apertures, the two lateral ones of which we 
have spoken, comprized. Such is, some few modifications 
excepted, the general system of the circulation of the de- 
capods. 
The upper surface of the brain is divided into four lobes, 
the middle ones of which, furnish each, from their anterior 
edge, the optic nerve, which is carried directly into the 
pedicle of the eye, and is divided there into a multitude of 
threads, proceeding each to a corresponding facette of the 
