Order Lncernaricc. 533 



weaker muscular layers ; both of the above layers are 

 immediately subjacent to the outer wall, and terminate, at 

 the edge of the disc, in a marginal muscular band which, 

 with varying degrees of breadth and thickness forms a 

 complete ring passing outside the bases of the tentacles 

 and anchors, and constitutes the terminus of the oral side 

 of the disc : the tentacles are disposed in eight groups on 

 the oral face just within the margin of the disc, and at 

 eight points which alternate with the four partitions and the 

 four corners of the mouth ; in each group those of the outer- 

 most row are the oldest ; they are hollow,* open into the 

 general cavity of the body, cylindrical, slightly tapering, 

 and terminate in a globular or spheroidal expansion which 

 serves a tactile purpose or as an organ of prehension : f 

 the intertentacular margin is either simple or at eight 

 points, exactly opposite the four partitions and the four 

 corners of the mouth, bears in youth a single tentacle, 

 which with increasing age, by the development of adhesive 

 vesicles in the outer wall, below the globose tip, becomes 

 more or less modified in shape and proportions, according 

 to the species, varying from pistilliform to broadly oval, 

 fabffiform or trumpet-shape, and serves as an organ of ad- 

 herence and progression, of the same nature as the base of 



* In Milne Edwards' description of the plates of Zoophytes belonging to the 

 third edition of Cuvier, PI. 63, fig. 1, and in Edwards and Haimes' Hist. Nat. Coral- 

 liers, Vol. 3, p. 456, the tentacles are represented to have closed cavities, with au 

 ampulla at the base, like the ambulacral tubes of Ecliinoderms; this I am con- 

 vinced is a mistake, the ampullae being merely the more or less thickened, lobu- 

 late projections between the bases of the tentacles, as I have fully proved for my- 

 self by examination not only of our common Lucernarian, Haliclystus auricula, 

 but also of the same species that Edwards had, viz. : Calvadosia campanulata 

 (Lucernaria campanulata Lamx.) 



t As I shall have occasion to speak of the radial and tlie transverse develop- 

 ment of the groups of tentacles, I give here a brief description of their taxis and 

 of the mode of its development. In a young Haliclystus auricula, not quite yg- 

 of an inch in diameter, there arc four tentacles in each tuft, — No. 1, the 

 oldest and outermost; No. 2 the next oldest; No. 2a the next youngest ; 

 and No. 3 the youngest. In another bunch on the same individual there 



1 



2 2a 



3 



