F. Cavers. 
that the Green, the Brown, perhaps also the Red, and more 
doubtfully the Blue-green Algae arose respectively from similarly 
coloured Flagellata; and that the various groups of Fungi have 
arisen independently from different Algal forms—though some 
fungal series may have come directly from Flagellata, However, 
Vuillemin (144) has pointed out that in our ignorance concerning 
the conditions under which the earliest forms of life appeared, we 
are hardly justified in assuming that photosynthetic organisms 
necessarily preceded heterotrophic organisms in time, and that 
from this point of view the nitrogen-fixing Bacteria have as good a 
claim as chlorophyll-bearing organisms to be regarded as the 
nearest living representatives of the earliest forms of life. We 
cannot, however, construct a series of existing forms connecting 
the Bacteria with the main autotrophic Algal phyla, though it has 
been suggested (Doflein, 40 ; Zuelzer, 158) that the Bacteria may 
have given rise, through the Spirochaetes, to the Flagellata. 
Starting from simple coloured autotrophic organisms, 
Brunnthaler (6) argues that the Red Algae are the most ancient 
group of plants, on the grounds that (i) the earliest plants were 
in all probability free-swimming Flagellate forms, and no such 
forms occur among the present-day Red Algae ; (ii) the red pigment 
of the Rhodophyceae is an adaptation to life in the deeper waters 
of the sea and in the dim light of the primitive world with its 
dense cloud canopy, since this pigment absorbs the rays in which 
that light would be rich; (iii) the present-day Red Algae show 
hardly any primitive types, and motile free-swimming reproductive 
cells are absent from the group. The Brown Algae would come 
next; that this is a younger group is indicated by the great diversity 
in structure of the reproductive organs, the constant presence of 
flagellate reproductive cells, and the adaptation of the brown 
pigment to the absorption of light more closely approaching in 
quality that of the bright sunlight reaching the surface of the 
present world, but still with an atmosphere richer in water vapour 
than that of to-day. Meanwhile, the primitive Red Algae had 
become adapted to the dim ancient light, and therefore restricted 
to the deeper sea, leaving the upper waters as an open field for the 
evolution of the new brown seaweed population. The Green 
Alga;, finally, are the youngest group to appear in the succession 
outlined by Brunnthaler, their green colour being an adaptation 
to the fuller light (richer in the less refrangible rays of the 
spectrum) of modern times; the early forms were marine, but 
after possessing the upper waters of the sea and invading estuaries 
they became adapted also for life inland in fresh water. According 
to Brunnthaler, there is no direct relationship between the present- 
day Algae and Flagellata, though the earlier Flagellates may have 
given rise to the Red Algae; the living Flagellata he regards 
as the termination of an ancient series of organisms which have 
evolved independently of the Algae. 
II —General Characters of the Flagellata. 
Without dealing further with such questions as these, it may 
be noted in passing that there is a good deal to be said against the 
assumption, which has frequently been made, that the Flagellata 
represent the most primitive of known organisms ; this claim may 
