158 Descriptions of Preparations. 



' calcareous ring^ of the Holothurioidea, and the ' vertebral 

 ossicles' of the Asteriae^ see Semper, /. c, pp. i6i— 163; Baur, 

 /. c, p. 18; Miiller, Anatom. Studien, 1850, p. 154. 

 For the compensatory relation which exists between the respiratory 

 trees and the ciliated infundibula upon the mesentery, see 

 Brandt, Prodromus, Fascic. i., 1835, p. 59, who, in describing" 

 the genus Chiridota, says, ' Respirationis organum ramorum 

 nullum, sed ejus loco corpuscula cylindrica, apice saepissime 

 fissa, illae mesenterii parti, quae primam secundamque in- 

 testini curvaturam retinet affixa/ See also Semper, I. c, 

 pp. 4, 132. For figures of these organs in the Synaptidae, 

 see Bronn, Die Klassen und Ordnungen des Thier-reichs, 

 Bd. ii,, Taf. xliv., fig. 13 ; Sars, I. c, tab. xv., xvi. 



48. Sea-Anemone [Actinia Crassicornis), 



Dissected so as to show its various external and internal organs. 



A VERTICAL section having been made through the entire length 

 of the sub-columnar body, one of the halves thus obtained has 

 been suspended, so as to show the direct continuity, firstly, of the 

 cavity of the stomach with the general cavity of the body, and 

 secondly, of the general cavity of the body with the cavities of the 

 tentacles. These latter organs are arranged in four rows, within 

 the circumference of the oral disc, which forms a low parapet 

 externally to them ; they are shorter than the diameter of the oral 

 disc, even when fully extended ; in this specimen they are not fully 

 retracted, the animal having, probably, been killed by the addition 

 of fresh water; and their natural short and conical form is well 

 seen. Each tentacle tapers somewhat abruptly to a point, appa- 

 rently under the action of the muscular fibres, which act as a 

 sphincter to the foramen in its apical extremity. The peristomial 

 disc, internally to the inner row of tentacles, is divided into two 

 concentric areae by a line of depression corresponding with the 

 strong oral sphincter, which is seen in section at the entrance of 



