1176 Wisconsin Academy of Sciences, Arts and Letters. 
1 B), then the colony has the diamond shaped outline. All 
gradations between these two conditions are found. The cells 
in a single coenobe are all the same size; but two coenobes may 
differ with respect to size of the constituent cells. This differ¬ 
ence results from differences in the age of the coenobe. Occa¬ 
sionally a colony is found whose cells are in two planes forming 
a pyramid with a three celled base and one cell for the apex 
(Fig. 1 C). 
These differences in colony form are due to differences in the 
manner of origin of the cells of a colony. According to West 
(42) multiplication takes place by the formation of four daugh¬ 
ter cells within a mother cell wall, the division of the mother cell 
contents being in two planes. This gives rise to the rectang¬ 
ular type of colony. In the formation of the pyramidal colony 
apparently the cleavages that formed the daughter cells have 
been not in two planes but in three. This pyramidal posi¬ 
tion of the cells suggests that the cleavage of the mother cell 
was not simultaneous but progressive. This view is strength¬ 
ened by our knowledge that progressive cleavage takes place 
in such nearly related forms as Scenedesmus acutus, S. quadri - 
cauda, S. obtusus, and Tetradesmus vnsconsinensis according 
to my results (36) (37); in Dictyosphaerium pulchellum Wood 
according to Senn (35) ; and according to Braun (7) in Pedi- 
astrum granulatum Ktzg. 
G. S. West (41) and W. West (42) emphasize the fact that 
there is always a division of the mother cells of Tetracoccus 
into four daughter cells. According to my observations, eight 
daughter cells are sometimes formed. Thus in Figure 1, 
Plate LXXXV, we have the remains of a mother colony showing 
two old cells and the daughter colonies derived from the divi¬ 
sion of live other cells, the old cell walls of the latter being still 
present. One of the cells of the mother colony has apparently 
been lost. Unfortunately this alga was not obtained in unial- 
gal culture, so that the percentage of eight-celled colonies formed 
could not be determined. It is probable that, as in Pediastrum.,, 
Coelastrum, and Scenedesmus , the colonies with the larger num- 
