2G0 
SUPPLEMENT 
five principal groups, of four each, corresponding to tlie base 
of the first four feet, and of the external jaw-feet. Moreover, 
one isolated branch is placed altogether in front, and fixed to 
the second jaw-foot, while another equally isolated corresponds 
to the last or fifth foot. These gills are compressed by 
elongated, cartilaginous laminae, mobile, and attached one to 
the basis of each foot, for the purpose of expressing the water. 
These laminae separate the groups of gills, and in each group 
there is one of these gills, the most external, which is fixed to 
the basis of the lamina, and like it, moveable ; the others, be- 
ing adherent to the body itself, have no proper movement. 
Two similar laminae, without gills at their base, are attached 
to the most anterior jaw-feet, and to the last jaw properly 
so called. 
The testa of the Crustacea also presents an anterior aper- 
ture below its edge and on each side of the mouth, for the 
issue of the water. 
In the Squillse the gills are visible, and can serve for loco- 
motion : they are situated under the body and behind, to the 
number of five pairs, annexed to some short fins, divided into 
two lobes, and formed of membranaceous laminae, ciliated on 
their edges. It is at thea'oot of the external lobe of these fins, 
and at its internal edge, that the gill, which is very compli- 
cated, and which at first sight resembles a thick pencil, is at- 
tached. M. Cuvier, who w T as the first to observe this organ, 
describes it thus : “ The gill is at first formed of a conical pe- 
duncle, composed of two vessels. There proceeds from it a 
range of cylindrical tubes, which go on diminishing from the 
base of this peduncle to its point, similar to the arrangement 
of the pipes of an organ. Each of these is curved, and forms 
a long conical and flexible tail, which itself bears a very nu- 
merous range of long floating filaments, like lashes. Each 
filament contains two vessels, each tail and each tube two 
likewise, as does the general peduncle. 
