1194 Wisconsin Academy of Sciences, Arts and Letters , 
the manner of cleavage of 8 . acutus and 8. quadricauda (37). 
In the former there is a change in the position of the primary 
cleavage plane so that the second cleavage planes, which are 
formed at right angles to it, are laid down at varying angles to 
the long axis of the mother cell; in 8. quadricauda the primary 
cleavage plane remains at right angles to the long axis of the 
mother cell. This causes the second planes, which are like¬ 
wise formed at right angles to the primary cleavage plane, to be 
formed parallel to the long axis of the mother cell. The 
elongation of the daughter cells is not always equal and when 
this does occur the alternating type of colony is formed. 
The number of horns in a four-celled colony varies. Norm¬ 
ally there are four, one at each end of the terminal cells, but 
sometimes horns appear on the central cells. On account of 
this variability in the position of the horns Kirchner (22) has 
described certain forms which De Toni (39) calls varieties, 
but which Collins (151 and Migula (31) consider forms un¬ 
worthy of varietal rank. Besides the form typicus Kirchner 
recognizes setosus , in which there are projections on some of the 
median cells; horrid,us, with projections on all cells, and abund 
ans, with projections on the middle as well as the ends of the 
terminal cells. Migula (31) also includes with these forms 
Naegeli (Breb.) Babenh., which is characterized by pear- 
shaped cells that are irregularly arranged. I have found all 
of these variations in pure cultures from a single strain. The 
occurrence of one or more horns on the middle cells of the coe¬ 
nobe (setosus) is much more common that horns on all of the 
cells (horridus), or more than two horns on the terminal cells 
(abundans). 1 was unable to isolate any of these forms in 
pure or unialgal culture, a fact which suggests that the pres¬ 
ence of more than four horns in the coenobe is a variation that 
persists for a single generation only and is unworthy of being 
named. 
The presence of horns on the median cells of the coenobe is 
of interest from the morphogenetic standpoint. At one stage 
in the reproduction of the alga there are four daughter cell3 
arranged lengthwise within the mother cell wall. This group 
