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 Poecilopoda, and 

 Laemodipoda, the anterior, posterior, and lateral arterial 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 off, 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 roaearches of Treviranus 

 (Verm. Schrift, I. p. 78) upon Asellus, and of 

 Zenker (loc. cit. p. 21) upon Gammarus, the 

 arterial system is very rudimentary with tlie Iso- 

 poda, and Amphipoda. Tliis may be easily proved 

 by an examination of allied si)ecies. It may be aslied, 

 however, if the blood-currents of these Crustacea 

 are not enveloped in vascular walls so delicate as to 

 escape observation ; but with proper care one may 

 be satisfied that no such walls exist. From mus- 

 cular contractions or the bending of the articula- 

 tions, the current of the blood is often stopped, and 

 then the blood-globules evade the obstacle by 

 passing at any point directly from the arterial into 

 the venous current. 



Goodsir (Edinb. new Philoa. Jour. July, 1842, 

 p. 184) was certainly deceived when he affirmed that 

 he had observed the blood of Caprella circulating 

 in arterial and venous vessels. 



The absence of vascular walls with Caprella, 

 already observed by fViegmann (Arch. 1839, I. 

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

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

 cording to them, the circulation liere is analogous 

 to that of the Amphipoda.* 



s This disposition of the arterial system has 

 been observed by Aiidouin, Milne Edwards, and 

 Duvernoij (Ann. d. Sc. Nat. XI. 1827, p. 377, PI. 

 XXXII. and VIII. 1837, p. 33, PI. II. fig. 1), with 

 Squilla, while Mysis appears from its circulatory 

 organs to be allied to the Isopoda and Amphi- 

 poda ; see Thompson, Zool. Research, loo. cit. I. 

 p. 13, and Frey, loc. cit. p. 13. 



4 The arterial system of Mala and Homarus has 

 been described with many details in the so-often- 

 quoted memoir of Audouin and Milne Edwards 

 (Ann. d. Sc. Nat. XI. 1827, p. 352, PI. XXIV.- 

 XXIX.). Lund, also (Isis, 1825, p. 393, Taf. III. 

 fig. 1), has very well described the arteries of the 

 lobster. But especially' should be noticed the ex- 

 cellent preparations of Hunter of the arterial sys- 

 tem of this same animal (Catal. of the Physiol. Ser. 

 II. PI. XV.-XVIII.). For this system with the 

 crawfish, see Brandt, Med. Zool. loc. cit. p. 63, 

 Taf. XI. ftg. 2 ; and for that of Cancer pagurus, 

 Milne Edwards, in the Cyclop, loc. cit. p. 775, fig. 

 418. 



enters this organ without passing to the branchiae, 

 but the other portion traverses the gills and after- 

 wards returns to the heart." — Ed. 



* [ § 284, note 2.] In a private letter A^assiz 

 has communicated some interesting facts on the 

 circulation of Caprella. He says " Caprella has 

 a tubular, dorsal vessel with lateral valves, exactly 

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



front, into the main cavity of the body, moves back- 

 wards along the lower part of that cavity without 

 being enclosed in vascular walls, and returns to 

 the dorsal vessel through the lateral valves. The 

 circulation was traced in a livmg animal into which 

 a solution of a small quantity of carmine had been 

 injected." — Ed. 



