(After Iwanzov.) a, Undischarged nematocyst.
The cnidoblasts are the mother-cells of the nematocysts, each cell producing one nematocyst in its interior.
The entire nematocyst is enclosed in the cnidoblast which formed it.
When the nematocyst is completely developed, the cnidoblast passes outwards so as to occupy a superficial position in the ectoderm, and a delicate protoplasmic process of sensory nature, termed the cnidocil (cn) projects from the cnidoblast like a fine hair or cilium.
2.-I, Portion of epithelium from the tentacle of an Actinian, showing three supporting cells and one sense cell (sc); 2, a cnidoblast with enclosed nematocyst from the same specimen; 3 and 4, two forms of gland cell from the stomodaeum; 5a, 5b, epithelio-muscular cells from the tentacle in different states of contraction; 5c, an epithelio-muscular cell from the endoderm, containing a symbiotic zooxanthella; 6, a ganglion cell from the ectoderm of the peristome.
A large nematocyst, with everted thread, is seen in the right-hand ectodermal cell.