POLYZOA 



905 



an 



surrounded by a circle of tubular tentacles, which are clothed bv 



vibratile cilia ; these tentacles, in the species we are considering, 



vary from ten to twelve in number, but in some other instances they 



are more numerous. By 



the ciliary investment 



of the tentacles the 



Poly /COM. are at once dis- 



tinguishable from those 



hydroid polypes to 



which they bear a 



superficial resemblance, 



with which they 



at one time con- 

 founded ; and accord- 

 ingly, while still ranked 

 among zoophytes, they 

 were characterised as 

 citiobrachiate. The ten- 

 taciila are seated upon 

 an annular disc, which 

 is termed the lopJm- 

 />//<>,''. and which forms 

 the roof of the visceral 

 or perigastric cavity ; 

 and this cavity extends 

 itself into the interior of 

 the tentacula, 1 through 

 perforations in the lo- 

 phophore, as is shown at 

 J), tig. 687, representing 

 a portion of the ten- 

 tacular circle on a 

 larger scale, a n, being 

 the tentacula. b b their 

 internal canals, c the 

 muscles of the tentacula. 

 il the lophophore, and c 

 its retractile muscles. 

 The mouth situated in 

 the centre of the lopho- 

 phore, as shown at A, 

 leads to a funnel-shaped 

 cavity or pharynx, b, 

 which is separated from 

 the oesophagus, d, by a 

 valve at c ; and this oeso- 

 phagus opens into the 

 stomach, ?, which occu- 

 pies a considerable part of the visceral cavity. (In the Bowerbankia 



' Tin's communication between the tentacular anil visrcnil cavities is denied by 

 Dr. Vigelius, who has recently made a careful search for it. 



FIG. 687. Structure of Layuncula repvnx(\-M\ 



den). A, pi >lyi>ide ex [landed ; B, polypide retracted ; 

 C, another view of the same, with the visceral 

 apparatus in outline, that the manner in which it 

 is doubled oil itself, with the tentacular crown and 

 muscular system, may lie more distinctly seen : 

 a a, tentacula; b, pharynx; c, pharyngval valve: 

 iJ, oesophagus ; <-, stomach; /', it> pyloric orifice; 

 (/, cilia on its inner surface ; /;, biliary follicles lody < < 1 

 in its wall ; /, intestine ; k, particles of excremen- 

 titious matter ; /, anal orifice; ///, testis; 11, ovary; 

 o, ova lying loose in the perivisceral cavity; j), out- 

 let for their discharge ; q, spermatozoa in the peri- 

 visceral cavity ; /, s, t, it, r, n-, ,r, muscles. D, por- 

 tion of the lophophore more enlarged: a (^tenta- 

 cula; It b, their internal canals; c, their muscli--, : 

 J, lophophore ; 



its retractor muscles. 



