ON CRUSTACEA. 
259 
the root of the feet, under the lateral and inferior jut of the 
carapace. They repose upon two solid, oblique tables, of the 
interior of the body, which serve to close the lodges above, 
where the first muscles of the feet are fixed. The water can 
penetrate to them through a cleft which is behind this edge of 
the carapace, and issue out through an anterior aperture situ- 
ated near the mouth. In one genus, that of Dorippus, this 
anterior aperture, pierced in the body itself of the carapace, is 
very remarkable : their gills have each the form of a triangular 
pyramid, elongated, attached only by its base, and with the 
point directed upwards and inwards. They are composed of 
a stem of a cartilaginous nature, supporting numerous soft 
and membranaceous lamina?, separated into two longitudinal 
masses by a medial furrow, and piled one upon another, per- 
pendicularly to the axis of the stem which sustains them. In 
the furrow are found two thick vessels, one venous, the other 
arterial, which distribute their branches ad infinitum over the 
surface of the membranaceous and double laminae of the gills, 
so that the lymph there receives the impression of the respi- 
rable air mixed in the water. 
These gills are seven in number on each side, five depend- 
ing on the feet properly so called, and two on the first and se- 
cond jaw-feet. They are continually rubbed by two long thin 
cartilaginous and flexible laminae, attached near the base of the 
jaws, one above, the other underneath these organs; and the 
function of which appears to be, as M. Cuvier presumes, to 
express the water, which has served for respiration, from the 
intervals of the leaflets of the gills, so as to allow fresh supplies 
to enter. 
The gills of the decapod macrourous Crustacea differ from 
those of the brachyuri, in that the leaflets or respiratory 
laminae are replaced by cylindrical fdaments, disposed in tufts, 
which have each a vein and an artery. They are also much 
more numerous, being twenty-two on each side, divided into 
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