324 Dr. F. Cohn on a new genus of the family of Volvocineae. 



structure looks like a hollow glass globe with a ring formed of 

 eight green globules in its interior (figs. 1, 3). If the circular 

 line in which the centres of the eight primordiaUeells stand^ is 

 regarded as the equator of the envelope-cell, we ordinarily find 

 their position such that the equatorial zone lies parallel with the 

 plane of the object-glass, and the observer consequently looks 

 down upon the pole of the envelope-cell (figs. 1, 3, 14). In this, 

 the polar view, the eight primordial-cells stand in a perfect circle 

 and are placed very close to the circumference of the envelope- 

 cell. The distances between the primordial-cells are more or 

 less considerable according as they are proportionately larger or 

 smaller ; sometimes they constitute an elegant wreath composed 

 of eight large green rosettes, almost without any intervals 

 between them, or resemble an interrupted eight-angled star 

 (figs. 1, 14) ; sometimes the green globules are so far apart as to 

 look like the eight spokes of a wheel (fig. 3). The diameter of 

 a primordial-cell ^n the polar view amounts, in the former case 

 to y^^th of a line (0-013 mm.), in the latter to ^^^jth (0-0065), 

 — on an average to g-y^th of a line (0*0087 mm.). 



When, however, the whole revolves, so that the axis passing 

 through the two poles of the envelope-cell lies parallel with the 

 stage of the microscope, and the equatorial zone marked by the 

 eight green primordial-cells stands perpendicular to the latter, 

 consequently in the optic axis of the microscope, the envelope- 

 cell still looks like a circle, because it is a sphere ; but the eight 

 primordial-cells, lying in one plane, are then projected in a line 

 which corresponds to the diameter of this circle, so that the 

 whole resembles, under the microscope, a colourless disk cut in 

 half by a green zone (figs. 2, 4, 5). And in this, the equatorial 

 view, according to the position, the four primordial-cells in the 

 anterior hemisphere sometimes completely cover the four behind, 

 so that only four are seen altogether ; sometimes the latter ap- 

 pear through the interspaces between the former, and all eight 

 are seen in one line. This view also of course gives very dif- 

 ferent pictures according to the size of the primordial-cells and 

 the distance between them (PI. VI. figs. 2 & 4). 



Between the polar and equatorial views lie countless inter- 

 mediate positions in which the ring of primordial-cells, more or 

 less contracted, appears as an ellipse, with its longest axis con- 

 stantly in the diameter of the envelope- cell, while the shorter 

 axis appears longer or shorter, and the separate primordial-cells 

 are approached more or less towards each other according to the 

 laws of projection (figs. 9 & 10). 



Besides this difierence of the aspect which one and the same 

 individual afibrds merely in consequence of the different positions 

 resulting from its movements, a still greater variation is displayed 



