338 THE CRUSTACEA. $ 284, 
With the other Crustacea, with which the heart is unarticulated, the blood 
passes from this organ into arterial canals ; but the walls of these last sooner 
or later entirely disappear, so that here also the blood circulates at liberty 
between the interstices of the body. The regular arterial currents thus 
formed finally bend about and become those of the venous system. With 
the Isopoda, and the Amphipoda, perhaps, also, with the Poecilopoda, and 
Laemodipoda, the anterior, posterior, and lateral arterial trunks disappear 
after a very short course. : . 
With the Stomapoda, and Decapoda, the arterial system is pretty well 
developed, and can be traced even to its ultimate ramifications. With the 
first, the heart, at its anterior extremity, sends off a simple, pretty long 
aorta, which ramifies to the eyes and tentacles; while from its sides, pass 
off numerous arteries for the segments of the body and their appendages, 
and, posteriorly, a branch which extends to the very extremity of the 
tail. i , 
With the Decapoda, on the other hand, the heart has three anterior 
aortae, of which the middle one goes, almost unbranched, to the eyes, while 
the two lateral, belonging to the antennae, give off, in their course, branches 
to the cephalo-thoracic organs. The two hepatic organs, alone, have special 
arteries, which arise directly from the lower surface of the heart. Behind, 
there is a posterior aorta which, immediately after its origin, divides into 
a dorsal and an abdominal branch. The first of these, either simple as 
with the Macrura, or bifurcated as with the Brachyura, extends even to 
the end of the tail, sending off branches right and left. The second passes 
below, and is distributed principally to the feet, the pincers, the foot-jaws, 
and the maxillae.@ 
~~ 9, According to the researches of T'reviranus 
(Vernix Schrift, I. p. 78) upon Aselius, and of 
Lenker (loc.* cit. p. 21) upon Gammarus, the 
arterial system is Very rudimentary with the Iso- 
poda, and Amphipoda. This may be easily proved 
by an examination of allied species. It may be asked, 
however, if the blood-currents of. these Crustacea, 
are not enveloped in vascular wall so delicate as to 
escape observation ; but with proper .~re one may 
be satisfied that no such walls exist. #..™ mus- 
cular contractions or the bending of the articu'a~ 
tions, the current of the blood is often stopped, and 
then the blood-globules evade the obstacle by 
passing at any point directly from the arterial into 
the venous current. 
Goodsir (Edinb. new Philos. Jour. July, 1842; 
p. 184) was certainly deceived when he affirmed that 
he had observed the blood of Capredla circulating 
in arterial and venous vessels. 
The absence of vascular walls with Caprella, 
already observed by Wiegmann (Arch. 1839, IL. 
p. 111), has been confirmed by Frey and Leuck- 
art (loc. cit. p. 104, Taf. Il. fig. 19, 20), and, ac- 
cording to them, the circulation here is analogous 
to that of the Amphipoda.* 
enters this organ without passing to the branchiae, 
but the other portion traverses the gills and after- 
wards returns to the heart.” — Ep, 
* [§ 284, note 2.] In a private letter Agassiz 
fhas communicated some interesting facts on the 
circulation of Caprelia. He says “ Caprella has 
tubular, dorsal vessel with lateral valves, exactly 
dike the larvae of Insecta, — the blood is emptied, in 
8 This disposition of the arterial systera has 
been observed by Audouin, Milne Edwards, and 
Duvernoy (Ann. d. Sc. Nat. XL. 1827, p. 377, Pl. 
XXXII. and VIII. 1837, p. 83, Pl. IL. fig. 1), with 
Squilla, while Mysis appears from its circulatory 
organs to be allied to the Isopoda and Amphi- 
poda; see Thompson, Zool. Research. loc. cit. I. 
p. 18, and Frey, loc. cit. p. 13. 
4 The arterial system of Mata and Homarus has 
been described with many details in the so-often- 
quoted memoir of Audouin and Milne Edwards 
(Ann. d. Sc. Nat. XI. 1827, p. 352, Pl. XXIV.- 
XXIX.). Lund, also (Isis, 1825, p. 393, Taf. IIT. 
fig. 1), has very well described the arteries of the 
lobster. But especially should be noticed the ex- 
cellent preparations of Hunter of the arterial sys- 
tem of this same animal (Catal. of the Physiol. Ser. 
II. Pl. XV.—-XVIII.). For this system with the , 
crawfish, see Brandt, Med. Zool. loc. cit. p. 68, 
Taf. XL. fig. 2; and for that of Cancer pagurus, 
Milne Edwards, in the Cyclop. loc. cit. p. 775, fig. 
418. 
front, into the main cavity of the body, moves back- 
wards along the lower part of that cavity without 
being enclosed in vascular walls, and returns to 
the dorsal vessel through the lateral valves. The 
circulation was traced in a living animal into which. 
a solution of a small quantity of carmine had been 
injected.” — Ep. 
