90 



THE ECHINODERMATA. 



<^88. 



In the Echinidac, the heart is long,'^' and attached to the oesophagus. 



In Echinus, it has several saccular enlargements, and internally has a 

 cavernous aspect, due to numerous irreguUxrly arranged septa. At each 

 of its extremities there are two vascular rings. The two below are situated 

 on the top of the lantern and surround the ccsophagus, while the two 

 above surround the anus ; all belong probably to the arterial and venous 

 systems. One of these last sends oif five branches to the genital organs, 

 while the other receives one of the two trunks which pass along the whole 

 length of the intestinal canal. Two longitudinal vessels, which send off 

 branches right and left, pass between each of the five pairs of ambulacral 

 organs. These are, probably, a branchial artery and vein.''* 



In the Holothurinae, the vascular system, which is without a heart, is 

 very distinct. An aortal trunk arises from the vascular ring, which sur- 

 rounds the oesophagus, and ramifies upon the intestine and the genital 

 organs. By a reunion of these ramiticatious, a second trunk like a vena 

 cava, is formed. This divides into two arteries, which ramify upon the 

 branchiae, and from which arise two branchial veins, which return to the 

 aorta."'' With the Sipunculidae, and Echiuridae, thei-e is a main vascular 

 trunk, which, after sending oft' laterally small branches, passes along the 

 ventral median line, above the digestive canal. <^^' 



its relations with the I'est of the vascular system. 

 Moreover, he has tal^en for an isolated, special 

 sanguineous system belonging to the ambulacra, 

 the aquiferous system, which communicates dnectly 

 with th:; ambulacra, and which forms a third ring, 

 situated between the two sanguineous ones of the 

 mouth. 



Volkmann^s description (Isis 1837, p. 513) is 

 wholly ditferent. According to him, the vascular 

 trunks of the superficial ring, and which are 

 located in the furrows of the arms of Asteracan- 

 thion violaceus, send off laterally ambulacral 

 branches ; the oral ring, situated more deeply, 

 sends off brandies, which, passing through the 

 cavity of tlie body, go to tlie rays and ambulacra, 

 and freely communicate with the cavity of 

 these last. This same ring has also an anas- 

 tomotic connection with that of the bacli. Accord- 

 ing to this, the cuxulation occurs, lie thinks, in the 

 following manner : The heart sends the blood into 

 the superficial oral ring ; thence it passes by the 

 vessels in the fiu-rows of the arms into the cavity 

 of the ambulacra ; these last, acting as venous 

 hearts, send it, by the vessels in the interior of the 

 rays, to the second oral ring, from which it passes 

 to the tliird and dorsal ring, and thence to the 

 heart. 



It is evident that Volkinann has taken a part 

 of the aquiferous system for that of the sanguineous 

 one ; and it is probable that he did not observe the 

 second oral ring. No correct idea can be formed 

 of the distribution of the arteries and veins of the 

 Asteroidae, or of their vascular system in general, 

 except by carefully separating it from the aquifer- 

 ous system, and considering the fact that the blood- 

 vessels do not open into the ambulacral vesicles, 

 but probably are spread as a capillary net-work 

 upon then: walls. 



4 The heart of Echinus, which is accurately 

 described by Valentin (Monogr. &c. p. 92, PI. 



Vin.), is attached to the oesophagus by a kind of 



mesentery. 



5 These details are supported by Valentin (loo. 

 cit. p. 93), who has already added much to the 

 labors of Tiedemann and Delle Chiaje upon tlie 

 sanguineous system of Echinus, although, Uke his 

 predecessors, he has been deceived as to its con- 

 nections. 



The received opinions upon the circulation of 

 these Echinoderms are, therefore, hypothetical. The 

 nature of the five glandular organs, which Val- 

 entin has seen communicate with one of the two 

 vascular rings situated upon the lantern, is very 

 problematical (Monogr. A:c. p. 95, PI. VII. fig. 

 119, i. 120). 



G See Tiedemann, loc. cit. p. 15. The sanguine- 

 ous system of Synapta Duvernaea, as described 

 by Quatrefages (loc. cit. p. 58), corresponds, 

 properly, to the aquiferous system of Holothuria, 

 which Tiedemann also has taken for a special 

 sanguineous system of the skin and ambulacra. 

 Hereafter we shall notice further both of these sys- 

 tems.* 



7 For the sanguineous vascular system of Sipun- 

 culus, and Echiurus, see Grube and Krohn (Mai- 

 ler's Arch. 1S3T, p. 248 ; 1839, p. 350), also 

 Forbes and Goodsir (Froriep's neue Nut. No. 

 392, loc. cit.). The vascular trunk embraces Uiere 

 the nerve so closely, that care is necessary not to 

 overlook one, or confound both together. 



Quatrefages has found in the anterior part of 

 the body of Echiurus Gaertneri three heart- 

 shaped swellings of the blood system, namely, a 

 ventral heart upon the ventral vessel, a dorsal 

 heart upon the dorsal vessel, and a mesenteric 

 heart situated beneath the digestive tube. This 

 last communicates with the ventral heart by a 

 flexuous vascular canal, and with the dorsal vessel 

 by a small vascular ring ; see Ann. d. Sc. Nat. loc. 

 cit. p. 324, PI. VI. fig. 4. 



* [ § 88, note 6.] See, for the vascular system 

 of the Holothurioidea, Miiller (Arch. 1850, p. 

 229), who has carefully studied it w'th the larger 

 Synaptinae. He confirms Tiedemann\s observa- 



tion above quoted as to the general distribution of 

 the vessels, and especially as to the presence of a 

 splanchnic system, which, as is well known, Qwa- 

 trefages has supposed to be wanting. — Ed. 



