42 
Busk on Volvox globator. 
however, is not the case in the form of Volvox, which formed 
the subject of my paper, is sufficiently obvious. But it is 
nevertheless true, as I find from examination of Professor Wil- 
liamson's specimens, that his representation is, in certain cases, 
equally correct, as I shall afterwards explain. Another cir- 
cumstance also noticed by Mr. Williamson, and which, till he 
pointed it out particularly to me, had, though not altogether 
unnoticed, been disregarded, is the existence of delicate lines 
between the green granules, and dividing the wall of the Vol- 
vox into very regular hexagonal spaces, in the centre of each of 
which is placed one of the green granules. The former of these 
conditions— which, though I have never met with it myself 
distinctly in specimens from any other locality, seems to be 
sufficiently abundant in the neighbourhood of Manchester — is 
represented in figs. 15, 16, 17, 18, 19, 20. In these it will be 
seen that the central green body is surrounded, at variable dis- 
tances, by a tolerably thick, distinct membrane or wall, and 
that numerous irregular filaments, where they exist at all, 
extend from the central mass to this wall, and there terminate, 
and do not pass from one green mass to another, as in the 
usual form. Now, I explain the way in which the zoospore is 
thus modified, in this way : I regard the external membrane 
merely as the boundary-wall of the original zoospore, and, like 
the entire body, as composed of vegetable protoplasm ; and I 
believe that this peculiar appearance is produced by a great 
and unusual expansion of the interior of the zoospore (by 
endosmosis of fluid probably), by which the outer or periphe- 
ral layer is separated from the remainder and principal part of 
the mass, containing the chlorophyll and nucleus, or supposed 
nucleus, &c. Zoospores, in fact, in this condition might be 
said to be dropsical. That this separation of the wall from 
the contents arises in this way, and not, as Mr. Williamson 
says, from the shrinking of contents, is, I think, sufficiently 
obvious from several considerations, and is rendered very clear, 
if we trace the progressive stages of the hydropical enlarge- 
ment in one and the same Volvox, as I have done in the figures 
above cited. 
In this series it is easy to observe the earliest formation of 
the clear space up to the most extreme dilatation of which 
the cell is capable, owing to its contiguity with others. Of 
course when a number of cells are thus enlarged and mutually 
compressed, they assume an hexagonal form ; but this hexa- 
gonal arrangement must not, as it appears to me, be con- 
founded with another, to which I have before alluded, and 
which I conceive to be due to a different circumstance alto- 
gether. In fig. 15 of this series, some cells will be obseved 
