CRUSTACEA. 
156 
tacea they are annexed, in tlie shape of tufts, to five pairs of paddles 
(feet) placed under the post-abdomen. The under part of this pos- 
terior portion of the body is similarly furnished, in the others, with 
four or five pairs of bifid appendages. 
0 
ORDER I. 
DECAPODA. 
The head, in the Decapoda, is closely joined to the thorax, and 
covered with it by a shell, entirely continuous, but that most fre- 
quently exhibits deep lines dividing it into various regions which 
indicates the places occupied by the principal external organs*. The 
mode of their circulation presents characters which distinguish them 
from the other Crustacea. The circumscribed heart f , of an oval 
form and with muscular parieties, gives organs to six trunks of 
vessels, three of which are anterior, two inferior, and the sixth pos- 
terior. Of the three anterior arteries,The median — the ophthalmic — 
is distributed almost exclusively to the eyes ; the two others — the 
amtennaries — spread over the shell, the muscles of the stomach, a 
]>ortion of the viscera and the antennae ; the two inferior ones — the 
hepatics — transmit blood to the liver ; the last — the sternal — is the 
most voluminous of the three, and arises from the posterior part of 
the body, sometimes on the right side and at others on the left ; its 
chief course is to the abdomen, and to the organs of locomotion. 
It gives origin to a great number of large vessels, among which Ave 
should particularly observe the one called by M. Audouin and Ed- 
Avards the superior abdominal, because it arises from the posterior 
part of that artery, at a short distance before the articulation of the 
thoi’ax Avith the abdomen, vulgarly termed the tail, and because it 
oon dips into the abdomen — tail — where it divides into tAA'olarge 
* M. Desmarest, in his Ilistoire Naturelle des Crustaces Fossiles, and in his Con- 
siderations Generates sur la Classe des Crustaces, has presented us, in relation to this 
point, with an ingenious nomenclature, based on the concordance of the portions of 
the external surface of the shell with the organs they cover. But, in addition to the 
fact thfit the shell of several Decapoda presents no impressions, or has them nearly 
obliterated, these denominations may be replaced by others more simple, more fami- 
liar, and relating to these same organs ; as the middle or centre, the anterior and 
posterior extremities, the sides, &c. : it appears useless to increase our nomenclature 
in this case. 
t These observations are extracted from the excellent memoir of Messrs. Audouin 
and Edwards, published in the Ann. d'Hist. Nut., t. XI, 283 — 314, and 352 — 393. 
See also the Mem. du Mics. d'Hist. Nat,, where M. Geoffroy Saint-Hilaire has 
inserted the results of his curious researches on the solids, and on the circulation of 
the Lobster. 
