F, Cavers. 
less heterotrophic forms (with holozoic, saprophytic, or parasitic 
nutrition), while the members of the remaining four divisions are 
normally provided with pigments which make holophytic nutrition 
possible, though many of these are also capable of heterotrophic 
nutrition and may therefore be described as “ mixotrophic.” In the 
lowest of the colourless groups in Senn’s arrangement, the Panto- 
stomatinese, any portion of the body can ingest solid food by means 
of pseudopodia, while in all the remaining forms capable of holozoic 
nutrition such ingestion occurs only at certain definite points; the 
Pantostomatinean genus Multicilia has a spherical protoplast with 
numerous radially arranged flagella, but in all other Flagellata 
the body shows radial or bilateral symmetry, or may be asymmetrical, 
and the number of flagella is more limited. According to Senn, the 
Pantostomatineac have given rise to the lower Protozoa (Sarcodina); 
to the small Flagellate group Distomatineac with irregular bilateral 
symmetry and paired groups of flagella—this group forming a 
blindly-ending line; and to the very large group Protomastigineae 
which comprises about half of the known genera of Flagellata and 
shows great variety in form and structure. The Protomastigineae 
may be regarded as the common source of the Infusoria, Mycetozoa, 
Sporozoa, and perhaps also the Bacteria, on one hand, and of the 
four groups of pigment-bearing or “Algal” Flagellata on the other. 
Of these latter, the Chrysomonadineae and the Cryptomonadineae 
are, according to Senn, closely related but of independent origin; 
the Chrysomonadineae have brown chromatophores, produce oil and 
leucosin, and show affinities with the Brown Algae and the Diatoms, 
while the Cryptomonadineae produce starch, are variously coloured 
or in some cases colourless, and may have given rise to the Peri- 
diniales and the Green Algae. The two remaining groups, Chloro- 
monadineae and Euglenineae, differ from the other groups in having 
numerous green chromatophores ; there is a more definite periplast 
or firm outer protoplasmic layer; the contractile vacuoles are so 
situated and co-ordinated as to form a pulsating system opening at 
a definite point on the exterior; the product of assimilation is oil 
(Chloromonadineae) or paramylum (Euglenineae). In the Chloro- 
monadineae, which Senn derives from Monas - and Bodo-Uke. form 
among the Protomastigineae, the contractile vacuoles are aggregated 
at the anterior end of the cell and open to the exterior by a pore. 
Senn regards the Chloromonadineae as being too highly organised 
to serve as the starting-point for an Algal group as suggested by 
Luther and others (see below); but they have by further elaboration 
of the cell given rise to the Euglenineae, a blindly-ending line repre¬ 
senting the highest type of organisation found in the Flagellata and 
decidedly showing no Algal affinities, whatever may be said of the 
Chloromonadineae. The Euglenineae have, as compared with the 
Chloromonads, a more definite, often striated, and highly resistent 
periplast, and a gullet-like canal leading to a deep-seated vacuole 
into which a system of small and actively contractile vacuoles is 
drained. 
Apart from Senn’s compilation, the more comprehensive 
accounts of the Flagellata are contained in zoological works (18, 
19, 37, 40, 93, 138, 150), and much of the recent literature on the 
“ Algal ” form is published in zoological journals. The Peridiniales 
will be dealt with in this review, since this group includes decidedly 
Flagellate forms, and reference will also be made to certain other 
