100 MANUAL OP ZOOLOGY. 



numerous tentacles, usually retractile, arranged in alternating 

 rows, and amounting to as many as 200 in number in the 

 common Actinia. The tentacles are tubular prolongations of 

 the ectoderm and endoderm, containing diverticula from the 



Fig. 26. Actinidse, Tealia crassicornis, the Dahlia Wartlet. 



somatic chambers, and sometimes having apertures at their 

 free extremities. The mouth leads directly into the stomach, 

 which is a wide membranous tube, opening by a large aperture 

 into the general body-cavity below, and extending about half 

 way between the mouth and the base. The wide space 

 between the stomach and column- wall is subdivided into 

 a number of compartments by radiating vertical lamellse, 

 termed the 'primary mesenteries,' arising on the one hand 

 from the inner surface of the body- wall, and attached on the 

 other to the external surface of the stomach. As the stomach 

 is considerably shorter than the column, it follows that the 

 inner edges of the primary mesenteries below the stomach are 

 free ; and these free edges, curving at first outwards and then 

 downwards and inwards, are ultimately attached to the centre 

 of the base. Besides the primary mesenteries, there are other 

 lamellse which also arise from the body-wall, but which do 

 not reach so far as the outer surface of the stomach, and are 

 called ' secondary ' and ' tertiary ' mesenteries, according to 

 their breadth. The reproductive organs are in the form of 

 reddish bands, which contain ova and spermatozoa, and are 

 situated on the faces of the mesenteries. Most of the Actiniae 

 are dioecious, that is to say, the same individual does not 



