29 
Flagellata and Primitive Alga. 
leading to the lower Algae. The results of recent work, some of 
which it is proposed to summarise and discuss here, have in the 
main confirmed the views expressed by Klebs in his diagrammatic 
scheme of the phylogenetic relationships between Flagellata and 
Algae—with certain modifications arising from the discovery of 
new forms and the reinvestigation of forms whose structure and 
development had been imperfectly known—and have lead to great 
advances in our knowledge of the phylogeny of the Algae, and to 
striking changes in the classification of the Green Algae in 
particular. 
It is now generally recognised that a division of the Flagellata 
into forms referable to the vegetable kingdom (forms hearing 
chlorophyll, having a cell-wall of cellulose, and having no mouth 
or other means for ingesting solid food) and forms referable to the 
animal kingdom (forms without chlorophyll, without a cell-wall or 
with a wall not consisting of cellulose, and having a mouth or 
other means for solid ingestion) would be absolutely unnatural and 
could only be made by ignoring genetic relationships which are 
perfectly obvious. Moreover, such a division would leave out of 
account a large number of organisms which could not logically be 
placed in either division. A better criterion would seem to be 
afforded by the consideration that in the lowest organisms regarded 
as animals, somatic growth and reproduction by fission are marked 
by active mobility, the flagellate cells growing and dividing in this 
condition ; whereas in the lowest organisms regarded as plants, 
somatic growth and division are marked by stability, and 
the flagellate cells do not grow and divide but may conjugate 
and give rise to a sedentary zygote. We shall see, however, that 
even this criterion—which has led to the inclusion by zoological 
writers of the greater part or even the whole of the Flagellata in 
the animal kingdom as a class of the Protozoa—is vitiated by the 
occurrence of transitional forms through which certain Flagellate 
groups shade off almost imperceptibly into definitely Algal 
organisms. 
Assuming that the lower Algae have arisen from a Flagellate 
ancestry, the work of the majority of recent writers on the 
phylogeny of the Algae has been directed towards the tracing of 
the lines of descent leading from certain Flagellate groups to the 
lower Algae, and to the formulation of a system of classification 
which shall reflect the phylogenetic relationships thus disclosed. Of 
the four main groups into which the Algae have usually been divided, 
the Blue-green Algae are probably related in some way to the 
Bacteria, but the origin and affinities of both divisions of “ Schizo- 
phyta”are quite uncertain, though they are possibly of Flagellate 
origin; the Green Algae may he traced, through transitional forms, 
to at least two distinct sources among the green Flagellata ; the 
Brown Algae have similarly been shown, especially by quite recent 
work, to have arisen from certain Flagellata with brown chromato- 
phores ; while as regards the Red Algae there appears at present 
to be no better-founded view than that suggested by Klebs—that 
they may have arisen from Brown Algae. 
In recent speculations concerning the evolution of plants it 
has generally been assumed that the earliest vegetable organisms 
possessed chlorophyll and were autotrophic (photosynthetic) 
forms, their immediate ancestors being autotrophic Flagellates ; 
