311 ORGANS OF DIGESTION. 



and the residue is thrown out by the mouth. In most of 

 the soft flexible vaginated forms of zoophytes, or keratophy- 

 tes, the posterior part of the polypus, which is the surface 

 of attachment in the hydra, is perforated by a pyloric orifice 

 to allow the digested part of the food to pass backward into' 

 the circulating system, as shown by Cavolini in sertularia, 

 plumularia, campanularite, and most other forms. The 

 polypi in those vaginated forms of keratophytes are the only 

 parts of the fleshy substance of the body which come into 

 free contact with the surrounding element, and they con- 

 stitute highly irritable and sensitive sacs, the tentacula 

 surrounding the margins of which are generally provided 

 with vibratile cilia to produce currents, and attract prey 

 within their grasp. The whole digestive and circulating 

 cavities ramified through the body of these animals form an 

 approach to those ramified through the common cellular 

 substance of poriphera, but here there are no common vents 

 or fecal orifices. From the transparency of the polypi and 

 of their horny enveloping cells, we can easily perceive the 

 contained food while it is being digested, and that the excre- 

 mentitious residue is thrown out by the same orifice by 

 which it entered, while the digested nutritious portion is 

 successively transmitted backwards through the pyloric 

 orifice, to be circulated through the central fleshy cavity 

 pervading all the ramifications of the body. These move- 

 ments of the digested matter through every part of the 

 fleshy substance of keratophytes, appear to depend on in- 

 ternal vibratile cilia, as the movements of similar globules 

 in the tubular fleshy feet of echinoderma, and in many 

 other parts of radiated animals. The polypi of the alcyonella 

 have a distinct lateral anal termination of their digestive canal, 

 and they further approach to the vorticella in their double 

 series of tentacula, which are here provided with vibratile 

 cilia. The digestive polypi have a more complicated and 

 isolated structure, in the cellaria andflustra as in iheflustra 

 carbesia (Fig. 63.), where the stiff elastic tentacula (63. d.) 

 disposed in a campanulate form and furnished with vibratile 

 cilia, are supported on a dilated portion of the body like a 

 head, and where the alimentary cavity has not only a length- 

 ened cylindrical curved intestinal form, but is even provided 

 with a distinct coecal or glandular appendix (63 b.) opening 



