II 



ACTINOZOA 



which the substance of the colony is stretched hke a glove over a finger. 

 Spicules — often brilliantly coloured — are present as usual but, as will 

 have been gathered, they take, in Gorgonia, no part in the formation of 

 the axial rod. 



ZOANTHARIA 



This group includes the ordinary sea-anemones, so commonly seen 

 in rock pools or attached to the piles of piers. While agreeing in their 



Fig. 49. 



A Sea-anemone [Peachia) bisected transversely. A, Upper ; B, Lower half, eg. Ciliated groove ; 

 d, directive mesenteries : m, muscle of mesentery ; m./, mesenterial .filament ; s.m, muscles of 

 secondary mesenteries ; st, stomodaeum. 



general structure with Alcyonarian polyps they show characteristic 

 differences in detail. 



The individual polyps are normally of much larger size and as a rule 

 they do not form colonies. ■ They may reproduce asexually by budding 

 or by a process of fission from above downwards but the individuals so 

 arising separate from one another and lead an independent existence. 



The tentacles instead of being pinnate are simply conical : instead 

 of being eight in number they are numerous, and commonly arranged 

 in several rows. The stomodaeum is usually provided with two ciliated 

 grooves, on opposite sides, although in some of the more primitive anemones 

 there is only a single ventral groove as in the Alcyonarians (Figs. 49 and 



