34 
Busk on Vblvox glohator. 
dergo segmentation, as pointed out in the case of Vblvox — I 
believe first by Professor Williamson. This process com- 
mences and proceeds precisely as in the ova of animals — the 
contents dividing first into two, and then each of the halves 
into two, and so on, till the division becomes too minute to 
allow of the counting of the segments. It is to be remarked, 
moreover — and I think this has not been noticed before — that 
the bright spherical bodies multiply quite as rapidly, if not in 
a more rapid ratio, up to a certain point, than the segmenta- 
tion goes on, so that each segment of the still-dividing mass 
always exhibits two, three, four, or even more of these par- 
ticles (figs. 1, 2). Ultimately the segmentation ends in the 
formation of innumerable green bodies, which are closely 
packed round the periphery of the cell. These bodies, though 
perfectly defined, are not at first separated by any clear space, 
and each contains at least one of the bright spherules alluded 
to (fig. 3). By their mutual pressure, these soft corpuscles of 
course assume an hexagonal figure, and they are now about 
l-4000th of an inch in diameter, or rather more. As soon as, 
or even before, the segmentation commences, a distinct though 
delicate membrane, surrounding the embryonic mass, is quite 
evident, as described by Mr. Williamson ; and beyond this is 
usually to be observed a very delicate zone of apparently 
gelatinous matter, which is sometimes so delicate as to escape 
observation, but may, I believe, always be detected by the 
use of a solution of iodine. 
When the segmentation is completed, in the way above de- 
scribed, the embryo Volvox exhibits the appearance of a sphe- 
rical body composed of a transparent membrane lined with 
distinct, uniform-sized, contiguous hexagonal masses. It con- 
tinues to grow, and very soon clear lines become apparent 
between the green masses, which are thus very distinctly 
defined, retaining the same hexagonal form — each with an 
apparent nucleus, which is probably derived from the bright 
spherule contained in it, but as yet without brown spot, clear 
space (vacuole), or vibratile cilia. As the embryo continues to 
grow, the spaces between the green masses continue to in- 
crease ; the green bodies gradually lose the hexagonal form, 
and assume the appearance of the ciliated zoospore next 
to be described. They are now about l-3000th of an inch, or 
thereabouts, in diameter, and the embryo, detached from its 
parent, becomes a free Volvox in its interior. We have thus 
arrived at the complete Volvox, and from the mode of its for- 
mation it is apparent that it consists of a transparent wall 
lined with the green bodies, and hollow in the interior ; and 
also that it is surrounded, at all events while within the 
