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 
Fig. 46.—Transverse sec- 
tion through the body 
of <Adamsia  dia- 
phana, 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 solid 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. mesembryanthemum being vivi- 
parous. 
In some species the free edges of the mesenteries are pro- 
duced into long whip-like 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 Sugartia. 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. 
