Flagellata and Primitive Alga 
35 
1, G, H), which is of great importance as forming a connecting link 
between the Chloromonad genus Cliloramceba (Fig. 1, A—C) on one 
hand and the Algal group “ Confervales ” on the other. This group 
had been previously founded as a distinct series of Green Algae as 
the result of the work of Borzi (14, 15) and of Bohlin (10) on various 
genera which had formerly been included in the old groups of 
Protococcoideae, Confervoideae, and Siphoneae. These genera 
differ from other Green Algae in several characters besides the 
possession by the motile cells of two unequal flagella—namely, the 
presence of a large proportion of xanthophyll or carotin in their 
chromatophores (hence the name “Yellow-green Algae” has been 
given to the group) which are typically numerous and discoid ; the 
production of oil instead of starch as the visible anabolite; and 
the curious structure of the cell-wall in some genera, e.g., the 
unicellular Opliiocytium in which the upper part of the wall 
becomes detached like a lid, and the filamentous Tribonema in 
which each cell is bounded by the halves of two H-shaped pieces 
and the whole filament readily breaks up into fragments of this 
shape. Luther and Bohlin concluded that these forms had arisen 
independently of the remaining Green Algae, from the simpler 
types of the Flagellate group Chloromonadineas, e.g., Cliloramceba , 
through a transitional form like Chlorosaccus. On the other hand, 
Cliloramceba leads through forms like Vacuolaria (Fig. 1, D—F) to 
the more specialised Chloromonadinese and doubtless to the 
Euglenineae, which need not be further considered here. 
The genus Lenvenia (Fig. I, J to V), recently described by 
Gardner (48), appears to be related to Chlorosaccus and to form 
an interesting additional link in the chain connecting Cliloramceba 
with the “ Convervales.” The motile cells are at first pear-shaped, 
with two unequal flagella and two ovoid curved green chromato¬ 
phores (sometimes becoming four or eight by division); later the 
cell becomes amoeboid. Growth occurs in a resting condition—the 
motile cells come to rest, float to the surface of the water, become 
spherical, withdraw their flagella, and grow rapidly in size ; then 
the nucleus divides into as many as twenty, the chromatophores 
divide by constriction, and finally the whole interior divides up into 
zoogonidia, each appropriating two chromatophores and a nucleus. 
Under certain conditions the resting cells secrete a gelatinous 
substance causing them (to adhere together in stringy floating 
masses, in which they become spherical; and in this palmella 
stage division into zoogonidia occurs as in the ordinary growth 
stage. 
Pascher (112) has recently described a new genus of Hetero- 
kontae ( Pseudoietraedron , which superficially resembles the Proto- 
coccaceous genus Tetraedron but shows characteristic Heterokontan 
features—numerous discoid yellow-green chromatophores, pro¬ 
duction of oil instead of starch, cell-wall consisting of two portions 
fitting upon each other like a box and its lid. 
Adopting the terminology suggested by Pascher (113), the 
following arrangement of the Heterokontae may be proposed. It 
will be noted that the group is here divided into a series of orders 
which show a striking parallelism with the corresponding divisions 
of the Isokontae. The genera of the Isokontan groups are omitted. 
