§284. 



THE CRUSTACEA. 



337 



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

 resembling the following type.<^' 



3. This type, 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 Insecta, 

 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- 

 riosuyn 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 orifices 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 towards 

 the posterior extremity of the back, where they enter the heart. <^* 



n. fig. 1, and especially ^urfoMin and Milne Ed- 

 wards, Ibid. XI. 1827, p. 376, PI. XXXII. These 

 last naturalists liave very distinctly represented 

 the dorsal venous orifices of the heart just men- 

 tioned. 



5 With Branchipus, Artemia, Isaura, and 

 Apus, the heart which has several constrictions 

 and whose venous orifices are very apparent, occu- 

 pies the entire dorsal median line excepting in the 

 caudal extremity ; see Joly, Ann. d. Sc. Nat. 

 XIII. p. 239, PI. VIII. fig. 4, j., XVII. p. 307, PI. 

 IX. fig. 43, r. ; also Krohn, Froriep^s neue Not. 

 XLIX. p. 305, fig. 1, 2 ; and Zaddach, loc. cit. p. 

 17, Tab. I. fig. 17, C, Tab. II. fig. 4-14.* 



6 Although Treviranus (Verm. Schrift. II. p. 

 31, Taf. VI. fig. 6), and Kutorga (loc. cit. p. 18) 

 have, indeed, furnished some communications on 

 the heart of Lilhobius and Scolopendra, yet we 

 are really indebted for what is known of the struc- 

 ture of this organ with the Myriapoda to the excel- 

 lent researches of Newport ; see Philos. Trans. 

 XXIU. p. 272, PI. XUI. fig. 18-22 {Scolopendra), 



and fig. 25 (Scutigera). According to these in- 

 vestigations, the interventricular septa are scarcely 

 developed with the Chilognatha, although very 

 much 80 with the Chilopoda. 



1 An extra vascular circulation has been ob- 

 served with the Lernaeodea, by Nordmann (loc. 

 cit. p. 73, 98), and with the Caligina, by Picker- 

 ing and Dana (Isis, 1840, p. 205, 1841," Taf. IV.). 

 Jurine (loc. cit. p. 437, PI. XXVI. fig. 8), and, 

 with more exactness, yogt (loc. cit. p. 9, Taf. I. 

 fig. 10), have described the circulation with Argtt- 

 lus. For that of Daphnia, see Gruitkuisen, 

 Nov. Act. Nat. Cur. XIV. p. 403, Tab. XXIV. fig. 

 6 ; Perty, Isis, 1832, p. 725, and Ehrenberg, 

 Abhandl. d. Berl. Akad. 1835, p. 189, note. Zad- 

 dach. (loc. cit. p. 23, Tab. I. fig. 17) has repre- 

 sented in much detail that of Apus. In order to 

 be convinced of the entire want of vascular walls 

 with the lower Crustacea, there is perhaps no 

 species which will serve better than Argulus foli- 

 aceus whose body is wholly flattened and trans- 

 parent throughout.! 



* [ § 283, note 5.] See also Leydig, loc. cit. Sie- 

 Oold and K6lliker''s Zeitsch. III. p. 287 {Artemia 

 and Branchipus). — Ed. 



t [ § 234, note 1.] This statement of the com- 

 plete absence of true vessels in Argu/us, is con- 

 firmed by the researches of Leydig (loc. cit. 



29 



Siebold and KoUiker''s Zeitsch. U. p. 337) upon 

 this same species. His schema of the circulation 

 with these animals is as follows : " The blood is 

 thrown from the heart into the interstitial lacunae 

 of the organs ; thereupon it is collected in the 

 posterior portion of the heart ; a portion of it 



