338 THE CRUSTACEA. «§> 284. 



With the other Crustacea, with which the heart is unarticulated, the blood 

 passes from this organ into arterial canals ; butthe walls of these last sooner 

 or later entirely disappear, so that here also the blood circulates at liberty 

 between the interstices of the body. The regular arterial currents thus 

 formed finally bend about and become those of the venous system. With 

 the Isopoda, and the Amphipoda, perhaps, also, with the Poecilojioda, and 

 Laemodipoda, the anterior, posterior, and lateral avterial trunks disappear 

 after a very short course.'-' 



With the Stomapoda, and Decapoda, the arterial system is pretty well 

 developed, and can be traced even to its ultimate ramifications. With the 

 first, the heart, at its anterior extremity, sends off a simple, pretty long 

 aorta, which ramifies to the eyes and tentacles ; while from its sides, pass 

 off numerous arteries for the segments of the body and their appendages, 

 and, posteriorly, a branch which extends to the very extremity of the 

 tail.<3' 



With the Decapoda, on the other hand, the heart has three anterior 

 aortae, of which the middle one goes, almost unbranched, to the eyes, while 

 the two lateral, belonging to the antennae, give oft", in their course, branches 

 to the cephalo-thoracic organs. The two hepatic organs, alone, have special 

 arteries, which arise directly from the lower surface of the heart. Behind, 

 there is a posterior aorta which, immediately after its origin, divides into 

 a dorsal and an abdominal branch. The first of these, either simple as 

 with the Macrura, or bifurcated as with the Brachyura, extends even to 

 the end of the tail, sending off branches right and left. The second passes 

 below, and is distributed principally to the feet, the pincers, the foot-jaws, 

 and the maxillae.'^' 



2 According to the researches of Treviranus 3 This disposition of the arterial system has 



(Verm. Sdirift, I. p. 78) upon Axellus, and of been observed by Audouin., Mihie Edwards, and 



Zenker (loc. cit. p. 21) upon Gammarus, the Duvernoy (Ann. d. So. Nat. XI. 1827, p. 377, PI. 



arterial system is very rudimentary with the Iso- XXXII. and VIII. 1837, p. 33, PI. II. tig. 1), with 



poda, and Amphipoda. This may be easily proved Squilla, while Mysis appears from its circulatory 



fiy an examination of allied species. It may be asked, organs to be allied to the Isopoda and Amphi- 



liowever, if the blood-currents of these Crustacea poda ; see Thompson, Zool. Research, loc. cit. I. 



are not enveloped in vascular walls so delicate as to p. 13, and Frey, loc. cit. p. 13. 

 escape observation ; but with proper care one may i Tlie arterial system of Mala and Homarus has 



be satisfied that no such walls e.xist. From mus- been described with many details in the so-often- 



cular contractions or the bending of the articula- quoted memoir of Audouin and Milne Edwards 



tions, the current of the blood is often stopped, and (Ann. d. So. Nat. XI. 1827, p. 352, PI. XXIV.- 



then the blood-globules evade the obstacle by XXIX.). Lund, also (Isis, 1825, p. 393, Taf. III. 



passing at any point dii-ectly from the arterial into fig. 1), has very well described the arteries of the 



the venous current. lobster. But especially should be noticed the ex- 



(ioodsir (Edinb. new Philos. Jour. July, 1842, cellent preparations of Hunter of the arterial sys- 



p. 181) was certainly deceived when he affirmed that tem of this same animal (Catal. of the Physiol. Ser. 



he hud observed the blood of Caprella circulating II. PI. XV.-XVIII.). For this system with the 



in arterial and venous vessels. crawfish, see Brandt, Med. Zool. loc. cit. p. 63, 



The absence of vascular walls with Caprella, Taf. XI. fig. 2; and for that of Cancer pa^urus, 



already observed by fViegmann (Arch. 1839, I. Milne Edn-ards, in the Cyclop, loc. cit. p. 775, fig. 



p. Ill), has been confirmed by Frey and Leuck- 418. 

 art (loc. cit. p. 104, Taf II. tig. 19, 20), and, ac- 

 cording to them, the circulation here is analogous 

 to that of the Amphipoda.* 



enters this organ without passing to the branchiae, front, into the main cavity of the body, moves back- 

 but the other jjortion traverses the gills and after- wards along the lower part of that cavity without 

 wards returns to tlie heart." — Kd. being enclosed in vascular walls, and returns to 

 * [ § 284, note 2.] In a private letter Agassiz the dorsal vessel through the lateral valves. The 

 has communicated some interesting facts on the circulation was traced in a living animal into which 

 circulation of Caprella. He says " Caprella has a solution of a small quantity of carmine had beea 

 a, tubular, dorsal vessel with lateral valves, exactly injected." — Kd. 

 like the larvae of Insecta, — the blood is emptied, in 



