494 POLYZOA AND COMPOUND TUNICATA. 



brane, which closes its orifice, and which then becomes continuous 

 with the wall of the ahmentary canal ; this lies freely in the visceral 

 sac, floating (as it were) in the liquid which it contains. The fur- 

 ther details of the anatomy will be best understood from the exa- 

 mination of a characteristic example, such as the Laguncula repens ; 

 which is shown in the state of expansion at a. Tig. 246, and in the 

 state of contraction at b and c. The mouth is surrounded by a 

 circle of tubular tentacula, which are clothed with vibratile cilia ; 

 these tentacula, 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 their tentacula, the 

 Polyzoa are at once distinguishable from those Hydraform 

 polypes to which they bear a superficial resemblance, and with 

 which they were at one time confounded; and accordingly, 

 whilst still ranked among the Zoophytes, they were characterized 

 as Ciliohrachiata. The tentacula are seated upon an annular disk, 

 which is termed the "lophophore," and which forms the roof of 

 the visceral or perigastric cavity ; and this cavity extends itself 

 into the interior of^ the tentacula, through perforations in the 

 " lophophore." The mouth, situated in the centre of the " lopho- 

 phore," leads to a funnel-shaped cavity, or pharynx, h, Avhich 

 is separated from the cesophagus, d, by a valve at c ; and this 

 oesophagus opens into the stomach, e, which occupies a, con- 

 siderable part of the visceral cavity. In the Botverhankia, and 

 some other Polyzoa, a muscular stomach or gizzard, for the 

 trituration of the food, 'intervenes between the oesophagus and 

 the true digestive stomach. The walls of the stomach, h, have 

 considerable thickness ; and they are beset with minute follicles, 

 which seem to have the character of a rudimentary liver. This, 

 however, is more obvious in some other members of the group. 

 The stomach is lined, especially at its upper part, with vibratile 

 cilia, as seen at c, g ; and by the action of these, the food is kept 

 in a state of constant agitation during the digestive process. 

 From the upper part of the stomach, which is (as it were) 

 doubled upon itself, the intestine i opens, by a pyloric orifice/, 

 which is furnished with a regiilar valve ; within the intestine are 

 seen at k particles of excrementitious matter; which are dis- 

 charged by the anal orifice at I. Xo circulating apparatus here 

 exists ; but the liquid which fills the cavity that surrounds the 

 viscera, contains the nutritive matter which has been prepared 

 by the digestive operation, and which has transuded through 

 the walls of the alimentary canal ; a few corpuscles of irregular 

 size are seen to fioat in it. The visceral sacs of the difterent 

 individuals put forth from the same stem, appear to communicate 

 with each other. No other respiratory organs exist than the 

 tentacula ; into whose, cavity the nutritive fluid is probably sent 

 from the visceral cavity, for aeration by the current of water 

 that is continually flowing over them. 



326. Tlie production of gemnipe may take place either from 



