CCELENTERATA : ACTINOZOA. 



II"; 



circulation of the digestive fluids contained therein. The sole 

 digestive apparatus in the Adinozoa consists of a tubular 

 stomach-sac, whicli communicates freely with the outer world 



Fig. 29.— A Transverse section of an Aciinozoon. a Digestive sac; 3 Wall of the 

 Body : ?« Mesenteries connecting the stomach with the body-walls, and dividing the 

 space between them into a number of vertical compartments, B Transverse section 

 of a Hydrozod'ji, showing the single tube formed by the walls of the body, 



by means of the mouth, and opens inferiorly directly into the 

 general body-cavity. In most, the " perivisceral space " be- 

 tween the body-walls and the digestive sac is subdivided into 

 compartments by. a series of vertical lamellse, which are called 

 the "mesenteries" (fig. 30, b). Upon the faces of these 



Fig. 30. 



-Morphology of Actinozoa. Diagrammatic vertical section oi Actinia. 

 <; 5tomach-sa6 ; ^Mesentery; c Craspcdum ; rf Tentacle. 



are borne the reproductive organs in the form of band-like 

 ovaria or spermaria. 



Thread-cells, often of very complicated structure, are almost 

 universally present, some of the Ctenophora having been asserted 

 to be without them; and some of the Actinozoa are able to 

 sting very severely. 



