656 Blackman.— The Primitive Algae 
status than an Alga. While the Tetrasporine tendency has 
given rise to all the higher green plants, the Endosphaerine 
has only succeeded in producing the elaborate but puny 
mockery of them which we find in Caulerpa. 
The simplest forms exhibiting this tendency seem to be 
derived also from the motile unicellular Chlamydomonas type 
by loss of motility and by dependence on zoospore-formation 
in place of vegetative division, which is in direct opposition 
to the line of development of the Tetrasporaceae. 
All the three lines of evolution which we have now con¬ 
sidered seem clearly to diverge from Chlamydomonas , and this 
motile organism must be regarded as the real primitive form 
of green plant. 
Beyond the glamour which this position throws over the 
Chlamydomonads, an immense importance should be attached 
to obtaining as complete knowledge as may be possible about 
the biology, structure, and reproduction of form, in which 
we have the vegetative potentialities of all the different types 
of green actualities which have filled the earth and attained 
justification by natural selection. 
Section II. Chlamydomonas. 
This section will be devoted mainly to the consideration 
of the genus Chlamydomonas. This is so much richer in 
species, in varieties of life-history, of structure and of repro¬ 
duction, than the other genera in its family, that many mono¬ 
graphs have- been devoted to the investigation of it; and as 
knowledge of the Algae increases, the tendency is always 
towards emphasizing the importance of this genus. 
A typical Chlamydomonad as Chi. Steinii (Fig. 13), Goros., 
consists of a single oviform cell, which swims freely by two 
cilia projecting from the advancing narrow end. It has a 
clearly defined cellulose wall, within which is the solid proto¬ 
plast. The greater part of the cell is occupied by the single 
large basin-shaped chloroplast, a small region of colourless 
protoplasm being visible at the anterior end only. To this 
