526 



HYDROIDA ; SERTULARIAN POLYPES. 



when in search of prey, they extend beyond it. Each single 

 Polype resembles a Hydra in every important respect but this ; 

 the stomach, instead of being closed at the bottom, communi- 

 cates freely with the interior of the stem and branches; and 

 the membrane lining its sac may be regarded as a prolongation 

 of that which surrounds their cavity. The pulp contained in 

 the hollow stem, rather than the Polype itself, appears to be the 

 essential part of the animal ; for the latter is not only formed 

 subsequently to it in the first instance, but frequently dies, and 

 is reproduced by it. 



1177. Of all Zoophytic productions, the structures formed by 



the Sertularice and their allies 

 are the most graceful in their 

 appearance, and delicate in 

 their conformation. They 

 are very abundant on our 

 own shores, seeming to pre- 

 fer temperate to tropical cli- 

 mates ; and they constitute 

 a large proportion of what 

 are commonly, but incor- 

 rectly, denominated Coral- 

 lines.* They have generally 

 a plant-like aspect ; consist- 

 ing of a stem, attached at 

 its base (where it sometimes 

 diverges into root-like pro- 

 longations) to some larger 

 mass, and sending off its 

 branches above with extreme 

 and most beautiful regu- 

 larity. The cells are ar- 

 PIO. 721.-8EETULAKIAN POLYPES. ranged upon the sides of 



these, like the minute leaflets 

 of Mosses ; and it is not surprising, therefore, that by the older 



* The real Corallines are a much smaller group, probably of Vegetable charac- 

 ter. In general aspect, their stems have some resemblance to those of the Sertu- 



