66 ; 
and the Flagellata . 
Flagellata (sens. Klebs) and for this reason, that it contains 
just those organisms which approach closest to the lowest 
plants. Any battle to extend or restrict the territory of the 
plant must be fought out on the boundary to be drawn 
between the Algae and the Flagellata. 
It is thus impossible to treat critically the lower green 
Algae without giving some attention to the groups of Flagellata 
which adjoin them. That we are able to consider these 
in any satisfactory way is due almost entirely to Klebs, and 
the masterly quality and immense quantity of his work make 
a deep impression on any one who goes into the subject. 
In 1893 Klebs published his elaborate study of the organisms 
of this group ; and this account serves as a starting-point for 
all future work and speculation. In these ‘ Flagellatenstudien,’ 
Klebs maintains that this name corresponds to a natural 
group of organisms having certain characters in common. 
The critical characters are those relating (1) to structural 
organization, (2) to the manner of vegetative division, and (3) 
to the nature of the resting stages. 
1. Broadly speaking the Flagellates have the same type 
of organization as the lowest Algae—the Chlamydomonads— 
namely, a motile, more or less oval, solid protoplasmic body 
with a central nucleus and a specialized anterior end with 
two or more cilia and contractile vacuoles. The cell may be 
colourless or have green or brown chromatophores. 
In the peripheral envelope, however, we find a difference. 
Outside the protoplasm there may be a dead mucilaginous 
envelope, but there is no cell-wall as in the lower Algae. The 
protoplasm may be limited by a very thin specialized layer 
(periplast) or by a thick special layer (plasma-membrane) 
as in Euglena , but these are integral parts of the cell and 
divide with it, unlike a true cell-wall. Further, starch is not 
found, chloroplasts are usually discoid, and the nature of the 
wall permits amoeboid movements to occur. 
2. The division usually takes place in the motile stage, 
and is always longitudinal and of the nature of a slow con¬ 
striction into two halves starting from the fore end. 
