MANUAL OF ZOOLOGY 



SECT. 



is partly paralysed before ingestion by the nematocysts of 

 the tentacles, but the process is completed, after swallow- 

 ing, by those of the mesenteric filaments. Then, as the 

 captured animal lies in the stomach, the edges of the fila- 

 ments come into close contact with one another and 

 practically surround it, pouring out at the same time, a 

 digestive juice secreted by their gland-cells. 



Sea-anemones are dioecious, the sexes being lodged in 

 distinct individuals. The gonads ovaries or testes are 

 developed in the substance of the mesenteries (Fig. 52, 

 gon.), a short distance from the edge, and when mature, 



often form very noticeable 

 structures. The develop- 

 ment of Sea-anemones re- 

 sembles, in its main 

 features, that of Scyphozoa, 

 but there is no alternation 

 of generations. 



Two main divisions or 

 sub-classes of the Actinozoa 

 are recognised the Zoan- 

 tharia and the Alcyonaria 

 the former including the 

 Sea-anemones, the Madre- 

 pores and other Stony 

 Corals, and the horny 

 Black Corals ; the latter 



the " Dead mens' fingers," Red Coral, Organ-pipe Coral, 

 " Sea-fans " and " Sea-pens." The principal distinguishing 

 features of the two sub-classes are, that in the Zoantharia 

 the tentacles and mesenteries are usually very numerous, and 

 are arranged, as a rule, in multiples of five or six, and that the 

 tentacles are simple in form : while in the Alcyonaria (Fig. 54) 



FIG. 54. Corallium rubmm, portion of 

 colony. (After Lacaze-Duthiers.) 



