114 CE@LENTERATA. 
processes. The muscular processes are pressed closely 
against the mesogloea, to which their ends are probably 
attached. Ina general way the processes run parallel to 
the long axis of the animal though they are somewhat 
indefinite in arrangement. Similar processes of the endo- 
derm cells run in a circular direction, in a transverse plane. 
Fig. 48.—AN EcTODERM CELL, ENDODERM CELL, AND A 
NERVE CELL (After JICKELI) CONNECTED WITH 
A NEMATOCYST. 
Ectoderm Cell. Endoderm Cell. 
Vacuole, 
Muscular 
Process. 
__ Nucleus 
Cnidoblast. 
The interstitial cells lie at the base of the epithelial cells 
between their tapering ends. They appear in sections as 
simple rounded and nucleated cells. In the living animal 
they may be ameeboid. All over the body, but especially 
on the tentacles, the interstitial cells give rise to the 
cnidoblasts. These grow outwards between the epithelial 
cells till they reach the surface. They are large ovoid cells 
which develop in their interior a cyst containing a long 
thread with barbs at its base and a fluid. On stimulation 
the cyst, or zematocyst, discharges the thread or sting which 
has a paralysing effect on small animals. 
Other interstitial cells accumulate in a mass to form 
the germ-cells. The ¢est#is is a mass of these germ-cells 
covered by epithelial cells and situated under 
the tentacles. The ovary is a similar mass 
towards the aboral end of the animal. The spermatozoa 
are produced in great numbers by division of the germ-cells 
Reproductive. 
