85 



on its body. The result is a series of lobed discs like a pile 

 of saucers. This process is termed strobilisation, and the 

 hydra-tuba is now called a scyphistoma. 



In December these " saucers " are liberated in suc- 

 cession. Each is a free- swimming ephyra ; it turns over 

 and becomes a jelly-fish. 



The life- history illustrates alternation of generations or 

 metagenesis. 



CLASS ACTINOZOA OB ANTHOZOA. 

 ORDER ALCYONARIA. 



Alcyonium. 



Describe the general Appearance of an Alcyonium Colony. 



The colony basis is a whitish, more or less lobed and 

 pulpy mass (the ccenenchyme) from which the numerous 

 polyps project. It consists largely of dense mesoglcea 

 jelly which is developed extensively from the bases of 

 the polyps. 



The polyps have pinnate tentacles ; they are deeply 

 embedded in the mass, and arise from stolons or endo- 



dermal tubes within the mass. 







Describe the Structure seen in a Section cut through the Colony 

 Mass of Alcyonium. 



The coenenchyme jelly (mesoglcea) has a honeycombed 

 appearance ; it is traversed by the large coelentera of the 

 polyps and by the smaller endodermal tubes and cords 

 connecting them. Each coelenteron shows the eight mesen- 

 teries of the polyp. Numerous spicules are scattered 

 throughout the jelly substance. The spicules are most 

 abundant about the colony surface and around the polyps. 



When the projecting Part of an expanded Alcyonium Polyp 

 is examined under a Lens, what Structures are seen ? 



Eight pinnate and hollow tentacles surrounding the 

 mouth, the gullet (stomodseum), the eight mesenteries 



