A piece of a colony full of larvæ was placed before midday in an aquarium, which was kept in a shady verandah. Large numbers of larvæ were set free almost immediately. They measured about 2 mm. in length and were distinctly pear-shaped; each contained a pair of polypides, which occupied a comparatively small part of the interior, the whole of the broader half being hollow. The larvæ swam slowly, broad-end-first, by means of the cilia with which their surface was covered, occasionally gyrating on their long axis and always adopting an erratic course. Towards evening they showed signs of settling down, frequently touching the glass of the aquarium with their broad ends and sometimes remaining still in this position for some minutes. Many attempts were, however, made before fixation was completed, and this did not occur until after nightfall. By next morning every larva was fixed to the glass and had everted its two polypides. Unfortunately I was not able to trace the development further, but young compound colonies were found in which the secretion of the common investment had just commenced. The zoaria in these colonies measured about 1 cm. in diameter and already contained many polypides each.
Oka has described the development from the statoblast of the allied Japanese species. He found that each statoblast produced in the first instance a single polypide, and that the statoblasts, which were produced in autumn, lay dormant through the winter and germinated in spring. As the Sur Lake begins to undergo desiccation as soon as the "rains" cease, the statoblasts in it probably do not germinate until the break of the next "rains" about the middle of June. I have had dried statoblasts in my possession for over two years. Their cellular contents appear to be in good condition, although the cells show no signs of development; but they have not germinated in my aquarium, in which some of them have now been kept for more than six months.
The green cells of the common investment are peculiar bodies that deserve further study than it has yet been possible to devote to them. Each cell is of ovoid form, varying somewhat in size but as a rule measuring about 0.03 × 0.008 mm. There can be no doubt that these bodies represent a stage in the life-history of an alga[[BO]]. Diatoms, bacilli and other minute plants are often present in the membrane as well as the characteristic green cells, but do not form a constant feature of it.
[BC] Proc. Linn. Soc. N. S. Wales, xxxiv, p. 489 (1909).
[BD] Rousselet, Proc. Zool. Soc. London, 1907 (1), p. 254.
[BE] See Rec. Ind. Mus. v, p. 40, footnote (1910).
[BF] In specimens preserved in spirit they are apt to collapse and therefore to become somewhat concave.
[BG] Annandale, J. As. Soc. Bengal (n. s.) ii, p. 188, pl. i (1906).
[BH] See Michaelsen, Mem. Ind. Mus. i, pp. 131-135 (1908).
[BI] Braem (op. cit., p. 3, pl. i, fig. 1), has described and figured under the name P. fungosa var. coralloides, Allman, a dense form that somewhat resembles this phase of P. fruticosa but has become compacted without external pressure. It is, however, probably a form of P. repens rather than P. fungosa and differs in its broad statoblasts from any form of P. fruticosa. I have examined specimens of the same form from England.