§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 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 

 vrith the craw-tish ; I have fouud it deep red with 

 Apus, and violet with Gammarus. That of Pa- 

 linuTus is also pale red, according to Lund and 

 Schultz (Isis, 1830, p. 122-3). See also Nord- 

 mann, loc. cit. p. 73 (Achtheres) ; Joty, loc. cit. 

 p. 238 (Artemia) ; Zenker, loc. cit. p. 20 (^Gam- 

 marus) ; Frey, loc. cit. p. 21 (My.iis), and Carus, 

 Von d. aiisseren Lebensbeding. d. weiss-und Kalt- 

 blutigen Thiere, p. 80. 



1 The heart is round or ovoid, and its pulsations 

 quite frequent, with Daphnia, Lynceus, Poly- 

 phem.us, and Evadne, where it is situated at the an- 

 terior part of the back, and very easily seen (see the 

 figures of it given by Straus, Jurine, and Lovin, 

 loc. cit.). According to Tfordmann (loc. cit. p. 

 11), there is also a round heart in the cephalo- 

 thorax oi Ergasilus. Jurine (Hist. d. Monocl. p. 



57. PI. 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 to a 

 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 (Yergl. Anat. 1834, p. 166) to find it. 

 W'ith Argulus, 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, PI. XXVI.). With 

 Achtheres, Dichelestium, Chondracanthus , the 

 heart consists of a long cylindrical tube (ISord- 

 mann, loc. cit. p. 73, and Rathke, 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.* 



* [ § 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- 

 lation, or a heart, can scarcely be said to here e.xist, 

 but there are two points in the median line where 

 there is a valvular action, and which perhaps per- 



form the functions of this organ ; see Dana, Cali- 

 gus, &c., Amer. Jour. Sc. XXXIV. p. 257, PI. III. 

 fig. 6, a. 6, b. 



A corresponding structure has been found with 

 Argulus, by Leydig (loc. cit. Siebold and Kiilli- 

 ker's Zeitsch. II. p. 335, Taf. XIX. fig. 3), who has 

 given, moreover, many histological details upon the 

 circulatory system of these animab. — Ed. 



