378 MR. S. LE M. MOORE’S STUDIES 
defeated. There would be one way, and one way alone, of obviating 
this, viz. increase in the size of the cilia; and it is apparently to 
this that the exceptional length of Apiocystis cilia is to be ascribed. 
Moreover, the larger the ccenobium, the greater the difficulty it 
would experience in moving about among masses of alge; nay, 
we might expeet that, if of relatively great size, it would tend 
to become entangled in slimy matter of animal or vegetable 
origin which is so frequent in ponds; and to this it would be 
especially liable on accouut of the long cilia. Indeed, any one 
who has paid any attention to, say, Pandorína must often have 
seen its cilia entangled, and the ccenobia for a time to all intents 
motionless organisms. Suppose the Apiocystis to have been at 
some former time in this condition throughout the greater part 
of its life, the large coenobia able to move along through the water, 
but ever liable to entanglement, it might now be advantageous to 
the alga to fix itself, and thereby ensure a position duriug sun- 
light favourable to its metabolism by simply rising with its host 
among the disengaged bubbles of oxygen. In this way we can 
account for polarity in Apiocystis—for that distinction between 
base and apex which never shows itself in other Volvocinee. 
It is not proposed to place Apiocystis among the Pandorinee. 
Some botanists, disregarding the manner of its sexual reproduction, 
might perhaps view its sedentariness as justifying its exclusion 
irom Volvocinee proper, which latter might be distinguished as 
Holoccenobie ; and until lately I was myself inclined to follow 
this course. Having been led to reconsider my views, however, 
I think it would be well to define a third family, to be called 
Merocenobie, in which may be included Apiocystis and any 
other organism with occasional ccenobial phases. At the pre- 
sent time we do not know of such with certainty ; but Borzi* 
has recently figured and described under the name of Physocy- 
tium confervicola a vemarkable fixed al ga, evidently closely.allied 
to Apiocystis. lt has the peculiarities, especially interesting in 
view of the polymorphism described in this memoir, that its wall 
becomes gelatinous previously to the escape of the zoospores, 
and that it can live as a Gleocystis; moreover, its reproduction 
is isogamous. True, Borzi did not notice exserted cilia; but 
these, if very fine, might easily escape observation, or he might 
have chanced upon eciliate specimens alone ; indeed it is doubtful 
whether Physocytium wil be able to maintain its position as à 
* ‘Studi Algologici,’ p. 71, tab. vi. 
