Pleodorina illinoiensis Kofoid in Britain . 179 
in other parts of the American continent, as well as in Europe, Java 
and Ceylon : see below. 
In 1898, Kofoid described (10) an alga, chiefly from a flooded 
area on the banks of the River Illinois, to which he gave the name 
Pleodorina illinoisensis. It was associated with Eudorina elegans 
and Pandorina Moruni, as well as with many other plankton organ¬ 
isms, animal and vegetable, in shallow warm water. The colonies 
were ellipsoidal, consisting mainly of 32 cells, rarely of 16, still 
more rarely of 64. The shape was quite constant, the average size 
of the mature colony being 113 X 94//.; the youngest colonies on 
escaping, measured about 46 x 38//, the largest were 200 x 175//. 
The young cells varied in the earliest phialea stage from 3-5 to 5//, 
the vegetative cells from 9-5 to 16-8//, the gonidial cells from 15 to 
25// ; they were all spherical and arranged in the usual zones. Each 
colony had both types of cells, the vegetative being the four anterior 
ones; the diameters were usually in the ratio of 1 : 1|, and the 
largest and smallest of each kind were much the same as in the 
Harborne specimens. The gelatinous envelope had two layers and 
was often provided with protuberances at the posterior end (three 
are shown in pi. 34, Fig. 4) which Kofoid suggested to be the places 
of exit of the daughter-colonies. He observed similar protuberances 
on the Eudorina and Pandorina in the same material, but did not 
observe the escape of any of the daughter-colonies. In the Harborne 
material, as already stated, nothing was seen to bear out Kofoid’s 
suggestion. The eye-spots, Kofoid says, decreased in size from 
front to rear, but apparently all the “ gonidial ” cells (excluding the 
dead ones which were to be met with from time to time) were 
regarded as being of the same size. The rotation of the colonies 
took place in either direction, though “ right over to left ” is said 
to have preponderated. 1 The four anterior cells Kofoid considered 
to be almost purely “somatic”; in two cases, he says, they had 
degenerated, but in one case they had begun to divide, one of them 
being as yet undivided and the three others being in the two-celled 
stage. Further, in two instances Kofoid saw mature colonies in 
which four daughter-colonies smaller than the rest (and of 8 and 16 
cells respectively) were present “ at one pole,” he does not say 
which. This account reads as if paucity of living material or 
insufficient length of observation makes the conclusions uncertain. 
They agree exactly so far as they go with my results, but they rest 
1 Unless the observations are made under a high power, it is quite easy to 
imagine a change of rotation as the upper or lower surface comes into focus. 
