Pleodorina illinoiensis Kofoid in Britain. 175 
daughter-colonies at the phialopore. The mamelons which Kofoid 
found there he regarded as possibly the points of exit; but that this 
is untrue is shown by the fact that they could be seen in perfection 
in many colonies in which division of the cells had not even begun. 
When the first gathering was made, a number of plakeas of 
cells were seen swimming about in a way resembling that of a fly 
buzzing on a window pane. There were about 64 cells in each 
(58 were counted in one instance), but they were so crowded that it 
was not easy to be sure of the number. The cells were more or 
less pyriform with the narrow ends all directed to one side, on which 
also lay all the cilia. These were at once interpreted as micro¬ 
gametes (antherozoids), but none were seen in situ and for a long 
time no more could be found. Then the expedient was adopted of 
letting a little water containing a few thousands of the colonies 
nearly dry up ; on moistening this again it was found to comprise 
numerous colonies which had produced microgametes. But the 
greatest number were found in a mass of the alga which had been 
kept crowded for some days in distilled water in a beaker, and 
amongst these numerous free antherozoid-groups were also seen 
buzzing about in their characteristic way. The colonies of anthero¬ 
zoids were easily distinguishable under a low power by their pale 
colour; most of them had had 32 and a few 16 cells, and in many of 
these some of the cells still remained undivided. Very frequently 
the four anterior cells were unchanged, while among the rest of 
the cells 1 to 6 might also still remain undivided, though in the 
majority of cases all the 28 cells, or even rarely all the 32, had 
formed groups of antherozoids (Fig. 4). 
In certain cases fully-formed ordinary ccenobia occurred mixed 
with the antheridia in the same colony. The table given over page 
summarises the particulars of a few of these, but they were not 
numerous; only those in which the antheridia and coenobia seemed 
ready to escape were reckoned. 
Each microgamete was about 12-15^ long, had an elongated 
fusiform but changeable shape, was pale-greenish at the posterior 
end and uncoloured in the anterior half, where a minute but bright 
red eye-spot was situated just in advance of the middle ; it had two 
flagella of rather more than its own length at the forward end. 
The microgametes were seen in profile to be arranged more or 
less parallel to one another in a dense bundle (Fig. 9), with the 
ciliated ends usually directed towards the centre of the colony, and 
in plan 32 could be seen placed exactly as in the 32-celled plakea of 
