663 
and the Flagellata. 
from the type of Chi. longistigma in that the gametes before 
throwing off their walls begin to contract away from them 
at the posterior end and remain in this preliminary condition 
for some time, thus clearly marked as gametes. Klebs makes 
acute use of this visible character in his well-known experi¬ 
ments on the effects of conditions in inducing vegetative or 
sexual activity. 
When a vegetative Chlamydomonas-ct\\ is about to divide 
to form new individuals (the usual number in one mother-cell 
being four), it usually loses its cilia and becomes motionless, 
but this is not always so, and a mother-cell occasionally may 
be seen still moving after the four daughter-cells within it 
have acquired their new cilia. The movement is effected by 
the old cilia being still in continuity with the hinder end of 
the protoplast of the nearest daughter-cell. Such a condition 
(Fig. 13) is regular in one species of the closely allied genus, 
Sphaerella Butschlii, see Blochmann (’ 85 ). 
At some stage in their life-history all the species of Chla - 
mydomonas are considered to pass into what is known as the 
Palmella-condition, where the cilia, eye-spot and contractile 
vacuoles may be lost and the resulting non-motile cells secrete 
mucilaginous walls within which they slowly divide to form 
irregular aggregates encircled by swollen traces of successive 
mother-cell-walls. Unfavourable conditions tend to produce 
this condition which was at first taken to be a separate genus. 
We have apparently in this condition the beginning of a 
vegetative existence in the narrower non-motile sense such 
as we find predominating in the Tetrasporaceae. At intervals 
in the life-history in this family the cells escape from their 
walls, put out cilia, and return to the motile condition as 
zoospores. 
Formation of zoospores is then nothing but reversion to 
an ancestral type of vegetative existence for a biological 
advantage, and all the vegetative existence of the higher 
Algae is phylogenetically a new intercalation into the life- 
history of the motile Chlamydomonad which is permanently 
in the zoospore condition, though walled, and in which 
