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



Closterium (fig. 8). Finally the primordial-cell becomes con- 

 stricted, gradually from the periphery to the centre, in the 

 middle line, and is thus divided into two secondary cells, the 

 septum of which, in the position above assumed, runs from right 

 to left (in the diagrammatic figure 21 from a through mio b and 

 n). Each of the halves cut off by the division then expands 

 somewhat in the direction from left to right ; a new constriction 

 soon presents itself in the direction from above downwards (in 

 the diagram fig. 21 from c through m to d and n) ; when this is 

 complete, the originally globular primordial-cell is divided into 

 four quarters (figs. 8, 9). 



This process of constriction and cutting off is repeated once 

 more, each secondary cell becoming divided by a new septum 

 into two equal halves (fig. 10). The division takes place through 

 two of the largest circumferences, passing from before back- 

 wards, and cutting the points m and n through which the two 

 preceding septa passed : on the diagram fig. 21 these are repre- 

 sented by the circles e, f, m, n, and g, h, m, n. Since the origi- 

 nally globular primordial-cell has meanwhile only expanded in the 

 direction of the two axes going from above downwards and from 

 right to left, and is not enlarged in the third direction, from 

 before backwards, the whole presents the form of a flattened 

 spheroid, somewhat of the shape of one of our loaves (the shape 

 of a turban, or of the bowls used on the bowling-green), which 

 is divided into eight equal segments, meeting in the middle, by 

 four ellipses distant 45" from each other, and intersecting in the 

 axis of rotation (vide figs. 10, 13 & 21). 



This process of division, by which each primordial-cell pro- 

 duces in the first generation two, in the second four, and in the 

 third eight secondary-cells, is completed in the course of the 

 night, so that early in the morning, in the long summer days 

 even by 3 o'clock, we perceive each of the eight primordial-cells 

 divided into eight in the manner described (figs. 10, 11). The 

 generations produced in each case by this triple subdivison vary 

 in the duration of their lives and in their capacity of develop- 

 ment j the first two rapidly divide again, and therefore are, ac- 

 cording to Nageli's expression, mere ' transitional generations ' ; 

 the third alone arrive at complete development and persist a long 

 time as such; these form the ' permanent generation.' 



The process of division does not always take place simulta- 

 neously in all the eight primordial-cells of Stephanosphan^a ; we 

 not unfrequently find inside the same envelope-cell some pri- 

 mordial-cells still wholly unaltered, while others are already pre- 

 paring to divide into two, a third perhaps already into four, and 

 a fourth has already resolved itself into its eight secondary-cells 

 (vide fig. 8). Very often most of the primordial-cells are found 



