and the Flagellata. 669 
Chloromonads are nearer the latter but the cell-type with 
many yellowish-green chloroplasts is different, and recently 
a definite affinity has been suggested between these Chloro¬ 
monads and a special group of green Algae (cf. Sect. IV). It 
seems to me then most reasonable by exclusion to derive the 
Chlamydomonads directly from the Protomastigina. As 
transitional forms we have Pyramidomonas , and Polyblepharis 
which Wille places in the Chlamydomonadaceae, but which 
though little known seem to be somewhat more primitive 
than Chlamydomoncts and almost devoid of a cell-wall. 
Possibly they have been derived from green forms among 
the Chromomonads, but these suggestions must suffice here. 
It appears that no organisms of preponderating plant- 
characters have been evolved from the Englena type. Its 
bright green colour and its power of holophytic nutrition 
superficially suggest an algal nature, and these with its well- 
developed plasmatic membrane and its paramylum-grains, 
which though not starch are an allied substance, seem to 
show that it has evolved from the Protomastigina in the plant 
direction, so to speak, or rather in a parallel direction. Still, 
by a consensus of the critical characters, it is a Flagellate 
beyond question. Closely allied to Euglena are some colour¬ 
less forms, and Zumstein (’ 99 ) has just shown that Euglena 
gracilis itself may exist as a colourless saprophytic form. 
He finds that if a pure culture of Euglena gracilis be placed 
in a sugar-solution in the dark it multiplies abundantly and 
may become quite free from chlorophyll. When the organisms 
are replaced in pure water in the light, the culture develops 
chlorophyll and becomes green again and assimilates carbon 
dioxide. Thus either a saprophytic or holophytic nutrition 
can be maintained. Grown in the light in a medium rich in 
nutritive matter Euglena gracilis is, according to the author, 
colourless, which suggests that it prefers a saprophytic nutrition 
and only develops chlorophyll in order to obtain carbon by 
assimilation of carbon dioxide when other sources are scanty. 
Here we have the spectacle of a single species lightly passing 
backwards and forwards over the supposed dividing line 
