COELENTERATA 



67 



of the body. The nervous system consists of scattered ganglion 

 cells, chiefly in the peristome and tentacles. 



The free edge of the mesentery below the level of the 

 oesophagus is divided into three lobes; the middle one is 

 crowded with nematocysts and glandular cells, the outer lobes 



Pig. 46. — Transverse sec- 

 tion through the body 

 of Adamsia dia~ 

 pTuma, in the region 

 of the stomodaeum. 

 After the Hertwigs. 



1. The directive mesen- 



teries. 



2. Longitudinal muscle 



fibres in the mesen- 

 teries, cut across. 



3. The siphonoglyphs. 



A. Primary mesenteries, 



12. 



B. Secondary mesenteries, 



12. 



C. Tertiary mesenteries, 



24. 



D. Quaternary mesenter- 



ies, 48. 



are ciliated. When a piece of soUd food is swallowed, the 

 edges of several of the mesenteries come together and surround 

 it, and the secretion of the glandular cells helps to digest it. 



The sexes are usually separate, the generative cells arising 

 from the endoderm of the mesenteries (Fig. 45) ; the young 

 escape through the mouth, A. mesembri/anthemum being vivi- 

 parous. 



In some species the free edges of the mesenteries are pro- 

 duced into long whip-Kke processes, called acontia, armed with 

 nematocysts. These are protruded through the mouth or 

 through special pores in the body-wall called cinclides. They 

 are found in Sagartia. Occasionally there is a central pore in 

 the base of the body, and as a rule the tentacles are perforated 

 at their ends ; and in some of the deep-sea forms the tentacular 

 pores are large, in others the tentacles are reduced, the pores 

 only remaining as a circlet of holes surrounding the mouth. 



