A large nematocyst, with everted thread, is seen in the right-hand ectodermal cell.
(After Kleinenberg, from Gegenbaur.) access of water to the contents; when the cnidocil is stimulated it sets in action a mechanism or perhaps a series of chemical changes by which the plug is dissolved or removed; as a result water penetrates into the capsule and causes its contents to swell, with the result that the thread is everted violently.
B, The same, partially everted by eversion of the sides, as in the Nemertine proboscis and Gastropod eye-tentacle = pleurecbolic.
23 the proboscis is seen in an everted state; it is only so carried when feeding, being withdrawn when the animal is at rest.
A, Siphonal notch of the shell e, Everted buccal introvert (prooccupied by the siphonal boscis).