^ 87, 88. 



THE ECHINODERMATA. 



89 



CHAPTER VI. 



CIRCULATORY SYSTEM. 



§87. 



The vascular, sanguineous system of these animals is yet imperfectly 

 known. The constant confusion and imperfection of its descriptions are 

 probably due to the fact that it has not been carefully distinguished from 

 the respiratory system ; and also, as was true of the Acalophae, because it 

 has been confounded with the aquiferous system, which is usually pres- 

 ent/" 



From all the old and new researches upon this subject, it is evident that 

 all the Echinoderms have an isolated system of this kind, composed usually 

 of both an arterial and venous trunk, between which there is, in some spe- 

 cies, an organ like a heart. 



§88. 



In the Crinoi'dea, there is, at the base of the calyx, a heart-like saccu- 

 lus, from which pass off vessels into the central cavity of the arms, the 

 cirri, and the pedicle when it is present. From its centre, another vessel 

 is given off for the spongy axis of the cavity of the body.^'' 



The Asteroidae have three vascular rings, one of which is under the 

 skin of the back, while the other two are beneath, around the mouth. 

 Between these vascular rings there is a long muscular heart, which, united 

 to the calcareous pouch or cord, extends from the madreporal plate to the 

 mouth. 



It is probable that the Asteroidae, which have many of these plates, 

 have also many calcareous cords and hearts.'-* From these vascular rings 

 numerous other vessels are sent off, some to the stomach and its appen- 

 dages, and the genital organs, and others to the ambulacra and their vesi- 

 cles.'^* 



1 The extended, and in some respects contradict- 

 ory works of Tiedemann and Delle Cliiaje (loc. 

 cit. ; see, also, Meckel, Syst. d. vergleich. Anat. 

 v. p. 25 ; and Sharpey Cyclopsed. &c. II. p. 41) 

 have not, for reasons which may be stated, cleared 

 up this point. The same may be said of what 

 relates to the blood of these animals, for it has 

 been confounded in part with the ambulacral hquid 

 belonging to the aquiferous system. See Warner, 

 Zur vergleich Physiol, der Blutes, 1833, p. 28. 



The observations of Delle Chiaje (Memor. &c. 

 n. p. 345) and of Cams (Analekt zur Natur. u. 

 Heilkunde, 1829, p. 132, and Lehrb. d. vergleich. 

 zoot. 1834, p. 673) do not give correct ideas upon 

 the mode and direction of the circulation of tliese 

 animals ; for it is evident that they did not see it, 

 but only the vibratile phenomena of the aquiferous 

 system. 



1 The vascular system of Comatula and Pen- 

 tacrinus has become known through Heusinser 

 (Zeitsch. f. organisch. Physik. III. 1828, p. 373, 

 Taf. X. XI.) and Muller (Abhandl. d. Berl. Akad. 

 1841, p. 193, 236, Taf. V.). The membranous canal, 



situated beneath the nervous branches of the arm, 

 and directly above the calcareous articulations, and 

 the passage of which through the arm into the 

 calyx Muller (loc. cit. p. 233) has not been able 

 to clearly make out, is probably a blood-vessel. It 

 is yet unknown how the blood of these vessels is 

 distributed to the organs. 



2 As in Eckinaster Solaris, and Ophidiaster 

 mulliforis ; see Muller and Troschel, loc. cit. 

 p. 1.34. 



3 According to Tiedemann (loc. cit. p. 49, Taf. 

 VIII.), the lower extremity of the heart of Astro- 

 pecten nurantiacus opens into the vascular ring 

 which surrounds the mouth. This last sends arte- 

 rial branches to the stomach, the cocca, and the 

 genital organs ; the superior extremity of the 

 heart communicates in like manner with another 

 vascular ring upon the back, and which receives the 

 veins of the organs just mentione<l. From a third 

 and reddish vascular ring' situated directly under 

 the skin of the mouth, Tiedemann has seen pass 

 into each ray a vessel placed superficially in the 

 furrow of the ambulacra, but he did not ascertain 



