BIOLOGY.--The zoaria of the species of _Plumatella_ are found firmly attached to stones, bricks, logs of wood, sticks, floating seeds, the stems and roots of water-plants, and occasionally to the shells of molluscs such as _Vivipara_ and _Unio_. Some species shun the light, but all are apparently confined to shallow water.
Various small oligochæte worms (e. g., _Chætogaster spongillæ_,[BG] _Nais obtusa_, _Nais elinguis_, _Slavina appendiculata_ and _Pristina longiseta_[BH]), take shelter amongst them; dipterous larvæ of the genus _Chironomus_ often build their protective tubes at the base of the zoaria, and the surface of the zooecia commonly bears a more or less profuse growth of such protozoa as _Vorticella_ and _Epistylis_. I have seen a worm of the genus _Chætogaster_ devouring the tentacles of a polypide that had been accidentally injured, but as a rule the movements of the lophophore are too quick to permit attacks of the kind, and I know of no active enemy of the genus. The growth of sponges at the base of the zoaria probably chokes some species, but one form (_F. fruticosa_) is able to surmount this difficulty by elongating its zooecia (p. 219). A small worm (_Aulophorus tonkinensis_) which is common in ponds in Burma and the east of India as far west as Lucknow, often builds the tube in which it lives mainly of the free statoblasts of this genus. It apparently makes no selection in so doing but merely gathers the commonest and lightest objects it can find, for small seeds and minute fragments of wood as well as sponge gemmules and statoblasts of other genera are also collected by it. I know of no better way of obtaining a general idea as to what sponges and phylactolæmata are present in a pond than to examine the tubes of _Aulophorus tonkinensis_.
[Footnote BG: Annandale, J. As. Soc. Bengal (n. s.) ii, p. 188, pl. i (1906).]
[Footnote BH: See Michaelsen, Mem. Ind. Mus. i, pp. 131-135 (1908).]
I am indebted to Mr. F. H. Gravely, Assistant Superintendent in the Indian Museum, for an interesting note regarding the food of _Plumatella_. His observations, which were made in Northamptonshire, were unfortunately interrupted at a critical moment, but I have reproduced them with his consent in order that other observers may investigate the phenomena he saw. Mr. Gravely noted that a small green flagellate which was abundant in water in which _Plumatella repens_ was growing luxuriantly, was swallowed by the polypides, and that if the polyparium was kept in a shallow dish of water, living flagellata of the same species congregated in a little pile under the anus of each polypide. His preparations show very clearly that the flagellates were passing through the alimentary canal without apparent change, but the method of preservation does not permit the retractile granules, which were present in large numbers in the cell-substance of the flagellates, to be displayed and it is possible that these granules had disappeared from those flagellates which are present in the recta of his specimens. It is clear, therefore, either that certain flagellates must pass through the alimentary canal of _Plumatella_ unchanged, or that the polyzoon must have the power of absorbing the stored food material the flagellates contain without doing them any other injury.