572 BIOLOGY. 



3477. The tubes of the Tubularise appear to be 

 nothing else than the posterior extremity of the Polyp, 

 desiccated or dried. These tubes are not therefore the 

 product of an excretion, but the body itself. 



3478. On the contrary, the tubes of the Sertulariae 

 must be held as being a tegumental excretion, within 

 which the Polyp ramifies and produces ova-cysts. If the 

 naked Polyps resemble ova which are devoid of shells, 

 such as the roe or spawn of Pishes, then the Sertulariae 

 resemble ova surrounded by a tough skin, like those of 

 Rays and Serpents. 



The Radiated Polyps or Horn-corals are invariably 

 ramified and converted towards their interior into a com- 

 mon horny or stony mass ; so that the animals themselves 

 appear to have coalesced upon this into a common tegu- 

 ment or bark. They possess a stomach and ovaries sur- 

 rounding it, which open into the border of the mouth 

 between the rays. They thus increase by ova and ramifi- 

 cations. 



They therefore represent the class proper of the 

 Polyps. 



The tufted Polyps comprise the proper Corals or 

 Lithozoa, are in form and substance like the Acalephae 

 but with this difference, that the covering is mostly 

 lithoidal, while in many Acalephans, as the Porpitse, it 

 only appears as a cartilaginous disc or plate. 



3479. These Corals are true ova, having a perfect 

 calcareous shell, like that of the Bird. The gelatinous 

 animal which adheres within a wide-mouthed Madrepore, 

 e. g. JFungia, resembles a vitellus just hatched, and from 

 which the foetal envelopes have been developed. 



3480. The numerous tentacular filaments surrounding 

 the wide mouth resemble the shags of the chorion, which 

 accumulate around the orifice of the umbilical cord to 

 constitute a placenta in the higher animals. 



The Corals are brood-eggs inclosed within the uterus 

 of Nature or in the sea. The Coral-animals are an um- 

 bilical cord, treasured up for the embryo, while the 

 Tubulariae are only membranous vitelli, and the Gor- 

 goniac, ova with desiccated albumen. 



