575 
member of the Palmellaceae . 
the Alga would return to its normal state when placed in suitable surround- 
ings. This culture was kept under constant observation. In about ten 
days zoogonidia began to appear, and in fourteen days zoogonidia were 
being actively formed, the culture rapidly spreading over the sandstone. 1 
The cells from the old culture continued at first to form non-motile 
gonidia (Figs. 8 a, 9 a, b). The zoogonidia were formed from these non- 
motile gonidia, often while the latter were still within the parent cell, cases 
being frequent in which some only of the daughter-cells had formed 
zoogonidia (Figs. 8 b, 9 c). Four, eight, or even sixteen zoogonidia were formed 
within a single gonidium (Fig. 10). If four only are formed they are 9 /x 
long by 5 /x broad, while if eight or sixteen are formed they are 7 /x long by 
3 /x broad, so that macrozoogonidia and microzoogonidia occur, though the 
distinction is one of size only, as in other respects they are identical. The 
zoogonidia vary slightly in shape, being either cylindrical or more or less 
pointed at one end. They are biciliated, with a parietal chloroplast, which 
is granular and has a distinct pyrenoid (Fig. 12). 
When fully formed they escape from the mother-cell, the process 
occupying from ten to twenty minutes. Material examined in water at 
this stage shows at first zoogonidia closely packed within the mother-cell 
and lying close to the cell-wall. In a few minutes they begin to vibrate 
slowly, forcing themselves apart and thus distending the cell-wall. As the 
wall is gradually distended they begin to rotate in different directions, at first 
slowly, and then with increasing speed, straining the cell-wall more and 
more until finally it is ruptured, and the zoogonidia escape. These swim 
actively for some time with the ciliated pole forwards, after which the 
movements gradually cease and the cilia are withdrawn. On coming to 
rest, the cell becomes rounded, develops a wall, and at once forms two or 
four zoogonidia ; or it may increase in size and form eight zoogonidia 
(Fig 13). After repeated generations have been produced in this way, the 
zoogonidia finally settle down and divide by oblique fission, forming the 
typical vegetative cells (Fig. 15). 
Systematic Position of the Alga. 
The Alga just described belongs without doubt to the family Palmel- 
laceae. The form and size of the cells suggest comparison with those 
palmellaceous Algae which possess elongated cells. 
In the first place it is necessary to consider the Alga described by 
Harvey, 2 and subsequently by Cooke, 3 as Palmella Mooreana . This Alga 
has occupied a doubtful systematic position since its original description. 
1 Klebs, Bedingungen der Fortpflanzung bei einigen Algen und Pilzen, 1896, p. 60, states that 
Vaucheria repens produces zoospores when transferred from a solution of inorganic salts to water. 
2 Harvey : Manual British Algae, 1851, p. 178. 
3 Cooke : Brit. Fresh w. Alg., 1882-84, vol. i, p. 14. 
