Zoarium. The zoarium is recumbent or erect, and is formed typically either of zoœcia arising directly in cruciform formation from one another, or of zoœcia joined together in similar formation with the intervention of tubules arising from their own bases. Complications often arise, however, either on account of the suppression of the lateral buds of a zoœcium, so that the formation becomes linear instead of cruciform, or by the production in an irregular manner of additional tubules and buds from the upper part of the zoœcia. A confused and tangled zoarium may thus be formed, the true nature of which can only be recognized by the examination of its terminal parts.
Zoœcia. The zoœcia are tubular and have a terminal or subterminal orifice, which is angulate or subangulate as seen from above. Owing to this fact, to the stiff nature of the external ectocyst, to the action of circular muscles that surround the tentacular sheath, and to the cylindrical form of the soft inverted part, the orifice, as seen from above, appears to form four flaps or valves, thus
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Polypide. The alimentary canal is elongate and slender as a whole, the œsophagus (including the pharynx) being of considerable length. In Paludicella and Pottsiella the œsophagus opens directly into the cardiac limb of the stomach, which is distinctly constricted at its base; but in Victorella the base of the œsophagus is constricted off from the remainder to form an elongate oval sac the walls of which are lined with a delicate structureless membrane. Victorella may therefore be said to possess a gizzard, but the structure that must be so designated has not the function (that of crushing food) commonly associated with the name, acting merely as a chamber for the retention of solid particles. In this genus the cardiac limb of the stomach is produced and vertical but not constricted at the base. The tentacles in most species number 8, but in Paludicella there are 16.
Resting buds. The peculiar structures known in Europe as "hibernacula" are only found in this family. The name hibernacula, however, is inappropriate to the only known Indian species as they are formed in this country at the approach of summer instead of, as in Europe and N. America, at that of winter. It is best, therefore, to call them "resting buds." They consist of masses of cells congregated at the base of the zoœcia, gorged with food material and covered with a resistant horny covering.
The family Paludicellidæ consists of three genera which may be distinguished as follows:—
| I. | Orifice terminal; mainaxis of the zoœcium vertical; zoœcia separated from oneanother by tubules. | |
| [A. | Base of thezoœcia not swollen; no adventitious buds | Pottsiella.] |
| B. | Base of thezoœcium swollen; adventitious buds produced near the tip | Victorella, p. [194]. |
| II. | Orifice subterminal,distinctly on the dorsal surface; main axis of the zoœciumhorizontal (the zoarium being viewed from the dorsal surface); buds notproduced at the tip of the zoœcia | Paludicella, p. [192]. |
Of these three genera, Pottsiella has not yet been found in India and is only known to occur in N. America. It consists of one species, P. erecta (Potts) from the neighbourhood of Philadelphia in the United States.
Victorella includes four species, V. pavida known from England and Germany and said to occur in Australia, V. mülleri from Germany (distinguished by possessing parietal muscles at the tip of the zoœcia), V. symbiotica from African lakes and V. bengalensis from India. These species are closely related.