■^ 87j 88. THE ECHINODERMATA. 89 



CHAPTER VI. 



CIRCULATORY SYSTEM. 



§87. 



The vascular, sanguineous system of these animals is yet mperfectly 

 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 Acalcphae, because it 

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

 ent. <i> 



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 Crinoidea, 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 tliat 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- situated beneath the nervous branches of the arm, 



ory works of Tiedemann und Delle Chiaje {\oc. and directly above the calcareous articulations, ami 



cit. ; see, also, Meckel, Syst. d. vergleich. Auat. the passage of which through the arm into the 



V. p. 25 ; and Sharpey Cyclopsed. &c. II. p. 41) calyx Midler (loc. cit. p. 233) has not been able 



have not, for reasons which may be stated, cleared to clearly make out, is probably a blood-vessel. It 



up this point. The same may be said of what is yet unknown how the blood of these vessels is 



relates to the blood of these animals, for it has distributed to the organs. 



been confounded in part with the ambulacral Uquid 2 As in Echinaster solaris, and Ophidiaster 



belonging to the aquiferous system. See fVai^ner, multiforis ; see Müller and Troschel, loc. cit. 



Äur vergleich Physiol, der Blutes, 1S33, p. 28. p. 134. 



The observations of £)e//e Chiaje (Jlemor. &c. 3 According to Tiedemartn (inc. cit. p. 49, Taf. 



II. p. 345) and of Cams (Analekt zur Natur, u. Till.), the lower extremity of the heart of Astro- 



Heilkunde, 1829, p. 132, and Lehrb. d. vergleich, pecten aurantiacus opens into the vascular ring- 



zoot. 1834, p. 673) do not give correct ideas upon which surrounds the mouth. This last sends arte- 



the mode and direction of the circulation of these rial branches to the stomach, the coeca, and the 



animals ; for it is evident that they did not see it, genital organs ; the superior extremity of the- 



but only the vibratile phenomena of the aquiferous heart communicates in like manner with another 



system. vascular rfng upon the back, and which receives the 



1 The vascular system of ComaUila and Pen- veins of the organs just mentioned. From a third 



tacrinus has become known through Heusinser and reddish vascular ring, situated directly under 



(Zeitsch. f. organisch. Physik. III. 1828, p. 373, the skin of the mouth, Tiedemann has seen pass 



Taf. X. XI.) and Müller (Abhandl. d.Berl. Akad. into each ray a vessel placed superficially in the 



1841, p. 198, 236, Taf. V.). The membranous canal, furrow of the ambulacra, but h( did not ascertaia 



8^ 



