The same excellent observer attributes the emission of the anemone poison threads, which he considers hollow, to the injection of a fluid. In their quiescent state, he thinks they are drawn in, like the finger of a glove, and are forced out as the liquid enters their slender tubes. Possibly the polyp stinging organs may have the same structure. Notwithstanding their dangerous weapons, polyps are often infested with a parasite, the _Trichodina pediculus_, as shown in Fig. E, page 49, and it must happen that either this visitation is not disagreeable, or that the Trichodina is not influenced by the poison. As the plants in the bottles decayed, some of the animalcules died off and others appeared. In one bottle, containing decaying chara, _Paramecia_ abounded. The _Paramecia_, of which there are various species, have always been favourite objects with microscopists. The Germans call them "slipper animalcules," and they vary in size from 1--96"[7] to 1--1150". They are flat rounded-oblong creatures, with a distinct integument or skin, "through which numerous vibratile cilia pass in regular rows."[8] They are furnished with a distinct mouth, and adult specimens exhibit star-shaped contractile vesicles in great perfection. [7] The usual mode of giving dimensions is by fractions thus expressed: 1--96" means one ninety-sixth of an inch. [8] 'Micrographic Dictionary.' The swarm of specimens before us belong to one species, _Paramecium aurelia_, the _Chrysalis animalcule_, and they crowd every portion of the little water-drop we have taken up, and examined with a power of about one hundred linear. When they are sufficiently quiet a power of about four hundred may be used with advantage, and Pritchard recommends adding a little indigo and carmine to the water, in order to see the cilia more clearly, or rather to render their action more plain. The cilia are disposed lengthwise, and Ehrenberg counted in some rows sixty or seventy of them, making an aggregate of three thousand six hundred and forty organs of motion in one small animated speck. This number seems large, but although we have never performed the feat of counting them, we should have expected it to prove much greater. Unlike most animalcules they are susceptible of being preserved by drying upon glass, and we subjoin a figure from Pritchard, of one thus treated, in which the star-shaped vesicles are clearly seen. These curious organs communicate with other vessels, and, as we have previously stated, are probably connected with respiration and excretion. [Illustration: Paramecium aurelia. A dried specimen showing the vesicles.--_Pritchard._]