So long as the gizzard retains its spherical form the green cells and its other contents are prevented from entering the stomach by the movements of the cilia that surround its lower aperture, but every now and then, at irregular intervals, the muscles that form its outer wall contract. The chitinous lining although resilient and not inflexible is too stiff to prevent the lumen of the gizzard being obliterated, but the action of the muscles changes its contents from a spherical to an ovoid form and in so doing presses a considerable part of them down into the stomach, through the ring of the cilia. [Illustration: Fig. 38.--Optical section of gizzard of _Hislopia lacustris_, with contained green cysts, × 240.] The contraction of the gizzard is momentary, and on its re-expansion some of the green cysts that have entered the stomach are often regurgitated into it. Some, however, remain in the stomach, in which they are turned round and round by the action of the cilia at both apertures. They are apparently able to retain their form for some hours in these circumstances but finally disintegrate and disappear, being doubtless digested by the juices poured out upon them by the glandular lining of the stomach. In polypides kept under observation in clean tap-water all the cysts finally disappear, and the fæces assume a green colour. In preserved specimens apparently unaltered cysts are sometimes found in the rectum, but this is exceptional: I have observed nothing of the kind in living polypides. Cysts often remain for several days unaltered in the gizzard. Imperfect as these observations are, they throw considerable light on the functions of the gizzard in _Hislopia_. Primarily it appears to act as a food-reservoir in which the green cysts and other minute organisms can be kept until they are required for digestion. When in the gizzard certain organisms surrender a large proportion of the food-material stored up for their own uses, and this food-material doubtless aids in nourishing the polyzoon. Although the cysts in the gizzard are frequently accompanied by diatoms, the latter are not invariably present. The cysts, moreover, are to be found in the zooecia of polypides that have formed brown bodies, often being actually enclosed in the substance of the brown body. The gizzards of the specimens of _Arachnoidea_ I have examined contain cysts that resemble those found in the same position in _Hislopia_. _Hislopia_ is widely distributed in the southern part of the Oriental Region, and, if I am right in regarding _Echinella_, Korotneff as a synonym, extends its range northwards to Lake Baikal. It appears to be a highly specialized form but is perhaps related, through _Arachnoidea_, to _Victorella_. 27. Hislopia lacustris, _Carter_. _Hislopia lacustris_, Carter, Ann. Nat. Hist. (3) i, p. 170, pl. vii, figs. 1-3 (1858). _Norodonia cambodgiensis_, Jullien, Bull. Soc. zool. France, v, p. 77, figs. 1-3 (1880).