NEMATOCYST ( from Gk. villza, thread kkres, kystis, bladder). One of the lasso-cells, thread-cells, or nettling organs (enithr) of jellyfishes and other Ccelenterata, act ing as organs of offense and defense. These bodies are imbedded in the outer cellular layer or ectoderm of eelentei-ates. A nematocyst is an oval, tough capsule, tilled with a clear fluid, and invaginated at one end in the form of a hollow process which is prolonged into a long coiled hol low thread. The entire structure is developed in an interstitial cell called a cnidoblast, which, as it approaches maturity, migrates toward the sur face and becomes imbedded in one of the large ectoderm cells. At one point on its surface the cnidoblast is produced into a delicate proto plasmic process, the cnidocil or 'trigger-hair.' Any small animal on coining in contact with the lasso-cells of a jellyfish is stung. benumbed, or poisoned by them. Upon contact with one or many of these lasso-cells in the tentacles of a or hydra, or a physalia, the enidoblast suddenly contracts, and the pressure upon the stinging capsule causes an instantaneous eversion of the thread, at the base of which are minute sharp barbs. The threads also convey a poison
ous fluid, which benumbs the victim. In this way sea-anemones and coral polyps obtain their food, paralyzing and thus capturing quite large animals. even fishes. These poison lasso cells also occur in certain Protozoa, mollusks, and in sponges, and in a modified form exist in the skin of certain worms, both terrestrial and aquatic. They are in these worms minute still' rods, either coiled up in an irregularly spiral manner, or short and straight, contained in oval cells. They are shot out in numbers when the animal is irritated, but are not retractile. being projected clear from the skin. That they are true nettling organs is proved by the fact that on touching the worms with the tongue they cause a tingling sensation. See illustration under C(ELENTERATA.