174 
W. B. Grove. 
bright-red colour until the colony was nearly ready to start off on 
its own career. It was not found possible to see the two eye-spots 
(the old and the new one) at the same time in the same cell, 
probably because the old eye-spot is necessarily in one of the 
posterior cells in which the new eye-spots are often absent or 
imperceptible. 
That eye-spots are really organs for the perception of light 
cannot be doubted. The presence of the largest eye-spots in the 
anterior cells and their regular diminution in size from front to 
rear are closely correlated with the definite forward motion. The 
young colonies, in which eye-spots are only beginning to he 
developed, are less decided in the direction of their movements than 
are the mature colonies. 
What has been described applies to the 28 cells not in the 
anterior row; the process of division was more or less simultaneous 
in them, although it always began in the posterior part of the colony 
and the more posterior cells usually completed it before the less 
posterior. 
In a very large proportion of cases the four smaller anterior 
cells underwent no division at all ; sometimes they began when the 
others had nearly completed the process, but in the majority of 
these instances they advanced only to the 16-celled plakea,of which 
the corners then rose up and formed a 16-celled phialea consider¬ 
ably smaller than the others in the same group. This was the way 
in which the 16-celled colonies (Fig. 2), occasionally to he seen 
swimming about, chiefly arose. Very rarely all the cells seemed to 
divide alike and more or less simultaneously. 
It was in these smaller colonies that the behaviour of the 
original eye-spot was most plainly to he seen. Since the cells from 
which they were formed had the largest eye-spots, when the 16- 
celled plakea was completed the eye-spot occupied a large fraction 
of the cell in which it lay, and it was equally conspicuous when the 
phialea was first formed ; yet, when these colonies became free and 
were on the point of swimming about, no eye-spots or only very 
minute ones (as the case might he) could ever he detected in them. 
The liberation of the daughter-colonies, which at that time 
measure about 35 x 27/x, from the mother takes place in Pleodo- 
rina exactly as it is known to do in Eudorina and Pandorina, by a 
slow dissolution of the mucous envelope. When first released, there 
is no essential difference between those of Pleodorina and of 
Eudorina. In no case was there ever seen an extrusion of the 
