§284. 



THE CRUSTACEA. 



339 



With all the Crustacea, the venous currents gradually converge from 

 the lower part of the body into various intercommunicating sinuses, situ- 

 ated, some upon the median line, and others at the base of the feet.® 

 From these sinuses the blood proceeds to the branchiae, and thence into 

 the dorsal sinus the walls of which are thin and uncontractile, and within 

 which the heart is entirely enclosed. This dorsal sinus is filled during the 

 systole, and the arterialized blood which it contains is absorbed during the 

 diastole through the venous orifices of the heart, without any aid on the 

 part of the walls of the sinus. <^ 



With the Myriapoda, also, the arterial system is highly developed. Not 

 only are there numerous arteries arising from the sides of the heart, which 

 ramify in the segments of the body, but also, beside an anterior dorsal 

 aorta, two other considerable arteries which embrace the oesophagus, then 

 bend below and unite to form, on the abdominal cord, a Supra-spinal artery. 

 This artery gives off numerous lateral branches, which accompany the 

 principal nerves, and terminate, at last, in ramuscules.*'"' 



But what distinguish the Myriapoda from the higher Crustacea, are 

 the venous currents, which, equally extra-vascular, do not run towards the 

 respiratory organs, but pass directly into the dorsal sinus, and thence are 

 absorbed into the chambers of the heart through the venous orifices.'*' 



5 Of the absence of vessels around the venous 

 currents one may easily be convinced from an ex- 

 amination of small Amphipoda and Isopoda. 

 This absence exists also with the higher Crustacea; 

 see Duverno!/, Ann. d. Sc. Nat. VIII. 1837, p. 

 34, or in Cuvier, Lemons d. Anat. Comp. VI. p. 

 401 (Sriuilla). I am quite of the opinion of Lund 

 and Sckultz (Isis, 1830, p. 1225), who have 

 combated the opinion of Audouin and Milne Ed- 

 wards and have described the venous system of 

 the Decapoda as having proper walls (Ann. d. Sc. 

 Nat. PI. XXVI.-XXXI.). liut Milne Edwards, 

 who, at this time, advocates with so much zeal the 

 wall-less condition of the circulating currents with 

 MoUusca, appears, moreover, to entertain the 

 opmion of a similar circulation with the Decapoda ; 

 at least, such would be inferred from what he has 

 said upon the circulation in general of Crustacea ; 

 see Hist. d. Crust. I. p. 101, and Cyclop, loc. cit. 

 p. 777. 



G According to Audouin and Milne Edwards 

 (loc. cit. PI. XXVI. fig. 3), the returning blood 

 from the branchi;ie enters the heart direct through 

 inter-anastomosing x)asa branchio-cardiaca. But 

 this statement has been reasonably doubted by va- 

 rious observers, for these naturalists had overlooked 

 the sinus which envelopes the heart of the higher 

 Crustacea, and receives, first of all, the branchial 

 blood ; see Straus, Consider. &c. p. 345 ; Lund 

 and Schultz, Isis, 1830, p. 1226; and Krohn, 

 Ibid. 1834, p. 522. This dorsal sinus has been 



compared sometimes to an auricle, sometimes to a 

 pericardium ; but, strictly speaking, neither of these 

 comparisons is correct. 



? The division of the anterior dorsal aorta, with 

 Scolopendra,\fas first noticed by Straus (Consider. 

 &c. p. 347). More detailed researches on the arterial 

 system of the same have been published by Ku- 

 torga (loc. cit. p. 18, Tab. III.), and Lord (Med. 

 Gaz. part VI. vol. I. 1837, p. 892), who were 

 chiefly occupied with the supra-spinal artery. But 

 of all the observers, Newport (Philos. Trans. 1843, 

 p. 274, PI. III. XIV.) has worked out the arterial 

 system of the Myriapoda in the most complete and 

 masterly manner. His researches have shown 

 that this system is least developed with the Julidae, 

 and rises gradually through the Glomeridae and Ge- 

 opliilidae — reaching its highest grade of structure 

 with the Soolopendridae. Kutonra has entirely 

 mistaken the nature of the heart in regarding it as 

 a vena cava, and the supra-spinal artery as an 

 aorta. Gaede, also (Zool. Magaz. I. p. 108, Taf. 

 I. fig. 7, g. f.), is quite in error as to the vascular 

 system of Scolopendra ; for he has evidently seen 

 the three vessels arising frum the anterior e.xtrem- 

 ity of the heart, namely : the dorsal aorta and the 

 two vessels which, uniting, form the supra-spinal 

 artery ; but he has taken them for nerves. 



8 Newport, who has so well observed the circu- 

 latory system of the Myriapoda, says nothing of 

 veins, and describes the dorsal sinus as a pericar- 

 dium. 



