680 



THE HYDROIDA AND THE SERTULARIAD^. 



our only known British form is the Tuft Coral. It is very rare, 

 and but seldom taken in our seas. The individual corals are about 

 half an inch in height and the same in diameter. 



We now arrive at the Hydroida, which are known by the internal 

 cavity being simple and the creature increasing by buds thrown out 

 from the sides. 



In the Sertulariadie the buds are enclosed in vesicles, and do not 

 break away when adult. They are in cup-like cells, which have no 

 footstalks. 



The reproduction of these beings is very curious, for it is known that 

 they can be propagated by cuttings just like plants, as well as by cell- 

 vesicles, and that in 

 the latter case the first 

 stage of the young 

 closely resembles that 

 of the young Medu- 

 sae, already mentioned. 

 They also reproduce 

 by offshoots, and it is 

 very likely that their 

 capabilitiGS in this re- 

 spect are not limited to 

 even these three meth- 

 ods. 



Any of the common 

 Sertularise affords a 

 good example of this 

 family, and, as they 

 are easily procured, 

 they are very valuable aids to those who wish to study the structure of 

 these beautiful beings. Even the empty polypidon is not without its 

 elegance, and is often made up into those flattened bouquets of so- 

 called seaweeds which are sold in such quantities at seaside bathing- 

 towns. But when the whole being is full of life and health, its mul- 

 titudinous cells filled with the delicate polypes, each furnished with 

 more than twenty tentacles all moving in the water, its beauty defies 

 description. These little polypes are wonderfully active and suspi- 

 cious. At the least alarm they retreat into their cells as if withdrawn 

 by springs, and when they again push out their tentacles it is in a very 

 wary and careful manner. 



ROTIFERA. 



Although the Rotifera, or " wheel animalcules," are generally placed 

 among the Infusoria, on account of their minute dimensions and 



The Cup Corals. 



