^ 284. THE CRUSTACEA. , 33T 



Phjllopoda, it is less elongated and has numerous constrictions, thereby 

 resembling the following type.''* 



3. This typ8, the third, is found with the Myriapoda, and considerably 

 resembles that of the so-called Dorsal Vessel of the Insecta. With the 

 Chilognatha, and Chilopoda, it consists of a more or less articulated tube, 

 occupying the whole dorsal line of the body. It is divided by constric- 

 tions and imperfect muscular septa into chambers, nearly as numerous as 

 the segments of the body. Each chamber is attached, as with the lusecta, 

 right and left to the internal surface of the, segments of the body, by tri- 

 angular muscles. The Diastole is produced chiefly through these muscles. 

 At its anterior extremity, this dorsal vessel passes through an Ostium arte- 

 riosufn into an aorta, while, from the posterior extremity of each of these 

 chambers are given off two lateral arteries. The returning blood enters the 

 heart through the two venous oriüces on the dorsal surface of each compart- 

 ment. The Systole consists of an undulating action from behind forwards, 

 and the blood is thereby propelled partly from one chamber to the next 

 forward, and partly into the lateral arteries.*''' 



§ 284. 



The Circulation outside of the heart, with the Crustacea, has very varied 

 relations, as has already been mentioned. With the lower Crustacea, with 

 the Siphonostoma, the Lophryopoda, and the Phyllopoda, the blood forms 

 regular currents in the intervisceral lacunae and interstices, but there is no 

 trace of vascular walls. The aortic current, shortly after leaving the heart, 

 divides into a right and left portion, which, also, sub-divide, enter the 

 appendages of the cephalic extremity, then turn and run along the abdom- 

 inal surface of the body — furnishing, in their course, several lateral, loop- 

 like currents, which enter the locomotive organs, then turn again toward» 

 the posterior extremity of the back, where tiiey enter the heart. '^* 



n. fig. 1, and especially Audoiiin anfl Milne Ed- and fig. 25 {Scutisera). According to these in- 

 wards, Ibid. XI. 1827, p. 376, PI. XXXIl. Tliese vestigaticins, tlie interventricular septa are scarcely 

 last naturalists have very distinctly represented developed with the Cliilugnatha, although very 

 the dorsal venous orifices of the heart just men- much so with the Chilopoda. 

 tioned. 1 An extra vascular circulation has been ob- 



5 With Branchipus, Artemia, Isaura, and served with the Lernaeodea, by Nordimnn (loc. 

 Apus, the heart which has several onstrictions cit. p. 73, 9S), and with the Caligin.a, by Picker- 

 and whose venous oriSces are very apparent, occu- in,? and Dana (Isis, 1810, p. 205, 1841, Taf. IV.). 

 pies the entire dorsal median line excepting in the Jurine (loc. cit. p. 437, PI. XXVI. tig. 8), and,, 

 caudal extremity ; see Jolt/, .\nn. d. Sc. Nat. with more exactness, i^ost (loc. cit. p. 9, Taf. I. 

 XIII. p. 239, Fl. VIII. fig. 4, j-, XVII. p. 307, PI. fig. 10), have described the circulation with Jrgu- 

 IX. fig. 43, r. i also Krohn, Froriep^s neue Not. lus. For that of Diphnia, see Gruithuiaeny. 

 XLIX. p. 305, fig. 1, 2 ; and Zaddack^ loc. cit. p. Nov. Act. Nat. Cur. XIV. p. 403, Tab. XXIV. fig. 

 17, Tab. I. fig. 17, C, Tab. II. tig. 4-14.* 6 ; Perty, Isis, 1832, p. 725, and Ekrenberg, 



6 Although Treviranus (Verm. Schrift. II. p. Abhaudl. d. BjrI. Akad. 1835, p. 189, note. Zad- 

 31, Taf. VI. fig. 6), and Kutorga (loc. cit. p. 18) dach (loo. cit. p. 23, Tab. I. tig. 17) has repre- 

 have, indeed, furnished some cjmmuiiicatioiis on sented in much detail that of Apus. In order to 

 the heart of Lithubius and Scolopendra, yet we be convinced of the entire want of vascular walls 

 are really indebted for what is known of the struc- with the lower Crustacea, there is perhaps ni. 

 ture of this organ with the Myriapoda to the excel- species which will serve better than Arffii/us foti- 

 lent researches of Newport ; see Pliilos. Trans, aceas whose body is wholly flattened and trans- 

 XXIU. p. 272, PI. XIII. fig. 18-22 {Scolopendra), parent throughout, t 



* [ § 283, note 5.] See also Leydig, loc. cit. Sie- Siehold and Külliker''s Zeilsch. 11. p. 337) upon- 



bold and Kolliker^s Zeitsch. III. p. 287 {Artemia this same species. His schema of the circulatioa 



Stall Branchipus). — Ed. with these animals is as follows: "T'le blood is 



t [ § 284, note 1.] This statement of the com- thrown from the heart into the interstitial lacunau 



plete absence of true vessels in Argulus, is con- of- the organs ; thereupon it is collected in the- 



firmed by the researches of Leydig (loc. cit. posterior portion of the heart ; a portion of it 



29 



