§ 2838. THE CRUSTACEA. 8385 
lacunae which lie between the different visceral organs and appendages of 
the body. But, notwithstanding the absence of vascular walls in these 
interstices, the blood moves in determinate directions, until, after a course 
of variable length, it is returned to the heart. During their course, the 
blood-currents are often taken up by particular reservoirs, which, as venous 
sinuses, may be regarded as forming the rudiments of the venous system. 
In this manner, notwithstanding the imperfection of this vascular appara- 
tus, all the organs constantly receive fresh blood, which is nowhere 
stagnant ; also, the arterial may be clearly distinguished from the venous 
currents, even when the arterial walls are wanting. 
The Blood, itself, is either, colorless, or of a faint red or violet hue. 
These colors belong to the blood-liquid, and not to the contained globules, 
which are few and always colorless. These globules are round, oval, or 
pyriform ; their surface is rough, and they contain fine granules, and, often 
a very large nucleus.” 
§ 283. 
The Heart of the Crustacea is always situated in the axis of the body, 
directly under the shell, at the anterior part of the back, and is often 
attached to the internal surface of the skeleton by muscular fibres. 
Usually, its walls are thin and composed of scattered muscular fibres 
interlaced in various ways. 
By the contraction of these fibres the blood is 
propelled from behind forwards through the arterial orifices, — those of 
the veins being closed at the same time by valves. 
The number of these different orifices, and the form and divisions of the 
Heart, have the following modifications : 
1. With many of the lower Crustacea, especially with the Siphonosto- 
ma, and the Lophryopoda, the heart is a simple, thin-walled sac, of 
either a spheroidal or an elongated form, but invariably with only two 
orifices, — a posterior or venous, and an anterior or arterial. 
1 For the blood-of Crustacea, see Wagner, Zur 
vergleich. Physiol. d. Blutes, p. 21. It is pale red 
with the craw-fish ; I have found it deep red with 
Apus, and violet with Gammarus. That of Pa- 
linurus is also pale red, according to Lund and 
Schultz (Isis, 1830, p. 1223). See also Nord- 
mann, loc. cit. p. 73 (Achtheres) ; Joly, loc. cit. 
p. 288 (Artemia); Zenker, loc cit. p. 20 (Gam- 
marus); Frey, loc. cit. p. 21 (Mysis), and Carus, 
Von d. atisseren Lebensbed i d Kalt- 
blutigen Thicre, p. 80. 
1 The heart is round or ovoid, and its pulsations 
quite frequent, with Daphnia, Lynceus, Poly- 
phemus, and Evadne, where ivis situated at the an- 
terior part of the back, and very easily seen (see the 
figures of it given by Straus, Jurine, and Loven, 
loc. cit.). According to Nordmann (loc. cit. p. 
11), there is also a round heart in the cephalo- 
thorax of Ergasilus. Jurine (Hist. d. Monocl. p. 
* [§ 283, note 1.] With Caligus, the circula- 
tion is wholly lacunal, and appears to consist of 
broad irregular streams, passing through the 
spaces left by the internal organs, — there being in 
no part distinct vessels. A single centre of circu- 
dation, or a heart, can scarcely be said to here exist, 
‘but there are two points in the median line where 
there is a valvular action, and which perhaps per- 
57. Pl. V. fig. 4) thinks he has observed a distinct 
auricle underneath the heart of Cyclops; but for 
my own part I have been unable to see it. As toa 
second or ventral heart, situated under the dorsal 
heart, which, according to Perty (Isis, 1832, p. 
725), is found with Daphnia, I have been as unable 
as Wagner (Vergl. Anat. 1834, p. 166) to find it. 
With drgulus, the heart is long and situated under 
the dorsal shell, as Vogt (loc. cit. p. 9, Taf. I. 
fig. 1,10, M.) has shown, contrary to the opinion 
of Jurine (loc. cit. p. 437, Pl. XXVI.). With 
Achtheres, Dichelestium, Chondracanthus, the 
heart consists of a long cylindrical tube (Nord- 
mann, loc. cit. p. 73, and Rathké, Nov. Act Nat. 
Cur. XIX. p. 153, and XX. p. 125). The anterior 
and posterior valvular system which Pickering 
and Dana (Isis, 1840, p. 206) have seen with Cali- 
gus, lead us to think that here also there is a heart 
between these valves.* 
form the functions of this organ ; see Dana, Cali- 
gus, &c., Amer. Jour. Sc. XXXIV. p. 257, Pl. III. 
fig. 6, a. 6, b. 
A corresponding structure has been found with 
Argulus, by Leydig (loc. cit. Siebold and Kélli- 
ker’s Zeitsch. II. p. 235, Taf. XIX. fig. 3), who has 
given, moreover, many histological details upon the 
circulatory systen. of these animals. — En. 
