^ 283. 



THE CRUSTACEA. 335 



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 tine 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 oftea 

 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 difi'erent 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 57. PI. V. fig. 4) thinks he has observed a distinct 



vergleich. Physiol, d. Blutes, p. '21. It is pale red auricle underneath the heart of Cyclops ; but for 



with the craw-fish ; I have found it deep red with my own part I have been unable to see it. As to a 



Apus, and violet with Gammarus. That of Pa- second or ventral heart, situated under the dorsal 



linurus is also pale red, according to Lund and heart, which, according to Perty (Isis, 1832, p. 



Schultz (Isis, 1830, p. 1223). See also Nord- 725), is found with Daphnia, I have been as unable 



mann, loc. cit. p. 73 {Achtheres) ; Joly, loc. cit. as IVagner (Vergl. Auat. 1834, p. 166) to find it. 



■p. lis (^Artemia) ; Zenker, loc cit. p. 20 {Gam- With ^rg-utes, the heart is long and situated under 



marus) ; Frey, loc. cit. p. 21 (Mysis), and Carus, the dorsal shell, as Fogt (loc. cit. p. 9, Taf. I. 



Von d. äusseren Lebensbediug. d. weiss-und Kalt- fig. 1, 10, M.) has shown, contrary to the opiuion 



blutigen Thicre, p. 80. of Jnrme (loc. cit. p. 437, PI. XXVI.). With 



1 The heart is round or ovoid, and its pulsations Achtheres, Dichelestinm, Chondracanthus, the 



quite frequent, with Daphnia, Lynceus, Poly- heart consists of a long cylindrical tube (Ttord- 



pAemus, and Eiiadne, where it is situated at the an- mann, loc. cit. p. 73, and Rathki, Nov. Act Nat. 



terior part of the back, and very easily seen (see the Cur. XIX. p. 153, and XX. p. 125). The anterior 



figures of it given by S«rau.s, [/"«rnie, and Zoi;^?!, and posterior valvular system which Pickering 



loc. cit.). According to Nordmann (loc. cit. p. and i)«»a (Isis, 1840, p. 206) have seen with Ca/i- 



11), there is also a round heart in the ceplialo- gus, lead us to think that here also there is a heart 



thora.^ ot Ersasiltis. Jurine (Hist. d. Mouocl. p. between these valves.* 



* [ ^ 283, note l.] With Caligus, the circula- form the functions of this organ ; see Dana, Cali- 



tion is wholly laounal, and appears to consist of gus, &c., Amer. Jour. Sc. XXXIV. p. 257, PI. III. 



broad irregular streams, passing through the fig. 6, a. 6, b. 



»paces left by the internal organs, — there being in A corresponding structure has been found with, 



no part distinct vessels. A single centre of circu- Argulus, by Ley dig (loc. cit. Siebold and Kolli- 



Jation, or a heart, can scarcely be said to here exist, ker''s Zeitsch. II. p. 335, Taf. XIX. fig. 3), who has 



but there are two points in the median line where given, moreover, many histological details upon the 



liiere is a valvular action, and which perhaps per- cLrculatory systen. of these .animals. — Ed. 



