Flagellata and Primitive Algce. 
3* 
perhaps quite as reasonably be put forward for bacterial forms or 
for the simpler amoeboid types of Protozoa. For instance, there 
are grounds for regarding a flagellum as a specialised type of 
pseudopodium, since between the blunt pseudopodium of an Amoeba 
and the vibratile flagellum of a typical Flagellate, there are various 
intermediate forms of protoplasmic outgrowth concerned in loco¬ 
motion or ingestion of food or other functions. In any case, how¬ 
ever, the Flagellata appear to include forms leading by a series of 
transitional types to the lower Green and Brown Algae, and these 
are our chief concern here. 
The characters given by Klebs as distinguishing the Flagellata 
from the motile unicellular Green Algae—the Chlamydomonads, 
which are still included by zoological writers in the Flagellata 
under the name “ Phytoflagellata ”—may be enumerated as 
follows. Body unicellular or a colony of cells, cell uninucleate 
with a thick or thin external layer of protoplasm—the periplast — 
in which amoeboid changes of form may take place. Outside this 
a non-living investment of the cell is frequently present, of varied 
form and often not closely adherent to the body. Specialised 
anterior end of clear protoplasm bearing one or more flagella. 
Organism always remaining capable of movement. Nutrition 
either holozoic (solid food being taken by pseudopodia, through a 
specialised mouth, or otherwise), saprophytic or holopliytic. In the 
last case the chromatophores are green or yellow-brown, and may 
take the form of bands, plates or discs. True pyrenoids entirely 
absent. Paramylum, leucosin, or a fatty oil the visible anabolites 
(products of assimilation). Starch entirely absent. Reproduction 
by simple longitudinal fission, usually beginning at the anterior end 
of the body. Individual always capable of forming resting cysts. 
Gamogenesis apparently entirely absent. 
It may be noted that recent work has made it extremely 
difficult to frame a definition of the Flagellata which shall separate 
this group sharply from the Protozoa on one hand and the lower 
Algae on the other. Exceptions have to be admitted in connexion 
with almost every character hitherto given in definitions of the 
group. The body usually has a definite anterior end from which 
one or more flagella arise, but in Multicilia the numerous flagella 
spring from various points of the spherical body; the flagella are 
usually motile and unbranched organs, but in certain Chrysomonads 
they are non-motile and even branched, corresponding with the 
pseudopodia of various Protozoa; the visible product of anabolism 
is usually either oil or leucosin or paramylum, but starch is formed 
in certain Chrysomonadineas (e.g., Cryptomonas ) and in the Polyble- 
pharidaceae (if these be regarded as Flagellates rather than Chlamy- 
domonadine Algae); the great majority are uninucleate, but the 
Trypanosomes have two nuclei, while Multicilia lacustris is described 
as having a large number; as a rule, division is longitudinal and 
occurs in the motile phase, but it is sometimes transverse (e.g., 
Oxyrrhis , Sty loch rysalis) and it may occur exclusively in a resting 
state; sexual reproduction is usually absent, but a sexual process 
has been shown to occur in various genera belonging to different 
groups of Flagellata (39, 50, 118, 121). 
In Senn’s account (135), which was published in 1900, the Fla¬ 
gellata fall into seven divisions. Three of these comprise only colour- 
