(5) Limnocodium kawaii, Oka (1907).
Oka, Annot. Zool. Japon. vi, p. 219, pl. viii (1907).
Only the medusa, which was taken in the R. Yang-tze-kiang, is as yet known.
(6) Limnocnida tanganyikæ, Bohm (1889).
R. T. Günther, Ann. Nat. Hist. (6) xi, p. 269, pls. xiii, xiv (1893).
Only the medusa, which is found in Lake Tanganyika, Lake Victoria Nyanza and the R. Niger, has been found and it is doubtful whether a hydroid generation exists.
(7) Polypodium hydriforme, Ussow (1885).
Morph. Jahrb. xii, p. 137 (1887).
Two stages in this peculiar hydroid, which is found in the R. Volga, are known, (a) a spiral ribbon-like form parasitic on the eggs of the sterlet (Acipenser ruthenus), and (b) a small Hydra-like form with both filamentous and club-shaped tentacles. The life-history has not yet been worked out[[AP]].
[AK] Similar capsules are found in the tissues of certain worms and molluscs, but there is the strongest evidence that these animals, which habitually devour cœlenterates, are able to swallow the capsules uninjured and to use them as weapons of defence (see Martin, Q. J. Micro. Sci. London, lii, p. 261, 1908, and Grosvenor, Proc. Roy. Soc. London, lxxii, p. 462, 1903). The "trichocysts" of certain protozoa bear a certain resemblance to the nettle-cells of cœlenterates and probably have similar functions.