§283. 



THE CRUSTACEA. 



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 Was^ner, 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 tlie 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 Gammnrvs. That of Pa- second or ventral heart, situated under the dorsal 



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



SchuUz (Isis, 18.30, p. 1223). See also Nord- 725), is found with £)«/iA«7"a, I have been as unable 



mann, loc. cit. p. 73 {Achtheres) ; Joly, loc. cit. as Wagner (Vergl. Anat. 18.34, p. 166) to find it. 



p. 238 (Artemia) ; Zenker, loc cit. p. 20 (Gam- With Argulns, the heart is long and situated under 



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



Von d. ausseren Lebeusbeding. d. weiss-und Kalt- fig. 1, 10, JI.) has shown, contrary to the opinion 



blutigen Thiere, p. 80. of Jurine (loc. cit. p. 437, PI. XXVI.). With 



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



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



;5Ae7«!(.?, and £iiarf?ic, where it is situated at the an- mann, loc. cit. p. 73, and Rathke, 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 67raMS, yMrj/ie, and Loi'i^Ti, and posterior valvular system which Pickering 



loc. cit.). According to Nord7nann (loc. cit. p. and Dayia (Isis, 1840, p. 206) have seen with Caii- 



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



thorax of Ergasilus. Jurine (Hist. d. Monocl. p. between these valves.* 



* [ § 283, note 1.] With Caligus, the circula- form the functions of this organ ; see Dana, Cali- 



tlon is wholly lacunal, 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. 



spaces 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 Leydig (loc. cit. Siehold and Kblli- 



latlon, or a heart, can scarcely be said to here exist, ker''s Zcitsch. 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 



there is a valvular action, and whic!'. perhaps per- circulatory system of these animals. — Ed. 



