194 DESCRIPTIONS OF PREPARATIONS. 



The so-called heart or plexiform organ (gland) is composed of a plexus of 

 vessels lying to the inner, i. e. adcentral, side of the stone canal inclosed in a peri- 

 haemal space. At its ventral end it is connected to a circumoral plexus which lies 

 in an incomplete septum dividing the circumoral perihaemal space into an outer and 

 an inner space. The radial vessels are similarly lodged between a right and left 

 space. At its dorsal end the plexiform organ is connected with a peri-anal ring which 

 gives off the ten vessels to the genitalia and two vessels, one on either side of its 

 dorsal end, to the intestine. These vessels are also lodged in spaces. The vascular 

 system contains brown cells, which also occur, but more sparingly, in the water- 

 vascular system. The perihaemal spaces are probably a part of the coelome. 

 They are lined by an epithelium which in the radial spaces forms an interrupted 

 ventral band of columnar cells which were supposed by Lange to be nervous. They 

 are said to communicate both with the coelome and the channels in the perisoma. 



The water-vascular oral ring lies to the dorsal and outer side of the two peri- 

 haemal spaces, and below or ventral to them is the thickened nerve-ring just as in 

 the arms. 



The coelome is lined by ciliated epithelium. 



Eckinodermata, Encyclopaedia Britannica (ed. ix.), vii. System der Asteriden, 

 Muller und Troschel, Brunswick, 1842. Stelle'rides du Muse'e, Perrier, A. Z. Expt. 

 iv. 1875 ; v. 1876. 



Species of genus Asterias, Bell, P. Z. S. 1881. 



Skeleton. Gaudry, A. Sc. N. (3), xvi. 1851 (for figure of Asterias rubens, PI. 18, 

 Fig. i); Agassiz, Memoirs Harvard Museum, v. 1877; Viguier, A. Z. Expt. vii. 

 1878. 



Names of ossicles belonging to ambulacral series. J. Muller, Abhandl. Akad. 

 Berlin (Classis Physica), 1853-54, p. 162 ; p. 210. 



Oral and apical system of Asteroids. Sladen, Q. J. M. xxiv. 1884 (contains 

 general references). 



Oral ossicles. Viguier, A. Z. Expt. vii. 1878; Ludwig, Z. W. Z. xxxii. 1879; 

 cf. remarks in Carpenter on ' oral and apical system of Echinoderms,' Q. J. M. xxii. 

 1882. 



Pedicellariae. Perrier, A. Sc. N. (5) xii. 1869. In Echinoids, Id. A. Sc. N. (5), 

 xiii. 1870; Geddes and Beddard, Trans. Roy. Soc. Edinburgh, xxx. ; Foettinger, 

 Archives de Biologie, ii. 1881 ; Sladen, A. N. H. (s)vi. 1880. In Euryalidae, Lud- 

 wig, Z. W. Z. xxxi. 1878. 



General Minute Anatomy. Beitrage zur Histologie der Echinodermen, Ha- 

 mann, pt. ii. Die Asteriden, Jena, 1885. 



Nervous system, eye, perisoma, feet, &c. Hamann, Z. W. Z. xxxix. 1883, p. 170. 



Mode of locomotion. Romanes and Ewart, Ph. Tr. 172, 1881, p. 836. Function 

 of eye and pedicellariae. lid. J. L. S. xvii. 1884, p. 131 ; cf. Romanes, Jelly-fish, Star- 

 fish, and Sea-urchins, Internat. Series, 1. 1885. 



Fission in Asteroidea and Ophiuroidea. Kowalewsky, Z. W. Z. xxii. 1872; 

 Simroth, Ibid, xxviii. 1877; Haeckel, Ibid. xxx. (suppl.) 1878; E. von Martens, 

 A. N. 32, 1866, p. 68. 



