158 



THE MICROSCOPE AND ITS REVELATIONS. 



FIG. 380. 



By the ciliary investment of the tentacles, the Polyzoa are at once dis- 

 tinguishable from those Hydroid polypes to which they bear a superficial 

 resemblance, and with which they were at one time confounded; and 

 accordingly, whilst still ranked among Zoophytes, they were characterized 

 as ciliobrachiate. The tentacula are seated upon an annular disk, which is 

 termed the lophophore, and which forms the roof of the visceral or peri- 

 gastric cavity; and this cavity extends itself into the interior of the tenta- 

 cula, through perforations in the lophophore, as is shown at D, Plate 



xxii., representing a portion of the 

 tentacular circle on a larger scale, 

 a a being the tentacula, b b their 

 internal canals, c the muscles of the 

 tentacula, d the lophophore, and e 

 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, Z>, 

 which is separated from the oeso- 

 phagus, d, by a valve at c; and this 

 oesophagus opens into the stomach e, 

 which occupies a considerable part 

 of the visceral cavity. (In the Bow- 

 erlankia and some other Polyzoa, 

 a muscular stomach or gizzard for 

 the trituration of the food inter- 

 venes between the oesophagus and 

 the true digestive stomach). The 

 walls of the stomach, h, have con- 

 siderable thickness; and they are 

 beset with minute follicles, which 



Cells of Lepralice.K, L. Hyndmanni; B, L. figu- seem to have the character of a 



lans; c, L. verruca. rudimentary liver. This, however, 



is more obvious in some other mem- 

 bers 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 regular valve; within the intestine are seen at Tc particles of excre- 

 inentitious matter, which are discharged by the anal orifice at I. No 

 special 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 float in it. The visceral sacs of the different polypides 

 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 perivisceral cavity, for aera- 

 tion by the current of water that is continually flowing over them. 



550. The production of gemmce or buds may take place either from 

 the bodies of the polypides themselves, which is what always happens 

 when the cells are in mutual apposition; or from the connecting stem or 

 'stolon,' where the cells are distinct one from the other as in Laguncula. 

 In the latter case there is first seen a bud-like protuberance of the horny 



