Busk on Volvox c/luhator. 
33 
of a transparent globe set with green spots, but il differs from 
the foregoing in two important respects. 
1. In the absence of any internal globules or embryos. 
2. In the irregular size of the green granules lining the 
wall, which, instead of being of a uniform size, are of various 
dimensions (fig. 13, PI. V.). The different sized granules are 
irregularly disposed, although, in relation to the sphere itself, 
they, or rather the centres of them, are as regularly dis- 
tributed as in the three just- described forms. What is rather 
remarkable with respect to this form is the circumstance, that 
the larger granules are not disposed over the whole periphery 
of the sphere, rarely occupying more than two-thirds of it, 
towards one side. In the more minute description of the 
elements of the above-mentioned organisms, the investigation 
of which requires the higher powers of the microscope, it 
will be convenient to commence with the common Volvox 
glohator; and as the tracing of the development of the internal 
embryonic globules affords the readiest road to a compre- 
hension of the true structure of the mature globe, I shall pro- 
ceed in that course. 
The internal embryonic globules are visible in the young 
Volvox while still within the parent ; but as they are at first 
concealed by the density of the wall of the young Volvox^ the 
very earliest stage of formation of the embryo cannot be 
readily noticed. In the earliest state in which these bodies 
can be observed, they appear as a globular, or rather discoid, 
nucleated cell (fig. 3), which, besides its apparent central 
nucleus, contains a number of minute spherules placed towards 
the periphery. At this time no distinct wall can be detected, 
the whole embryo (to use a convenient though incorrect term) 
apparently consisting of a homogeneous substance, with a 
lighter nuclear-looking space in the centre, and the above- 
mentioned spherules towards the periphery. This nucleated 
cell, as it may be termed, although without a cell-wall, in- 
creases in size, and the solid or coloured contents appear to 
retreat from the centre, which becomes clearer and clearer 
towards the periphery, which gradually becomes more and more 
opaque. As the cell grows, the nucleus (?) seems to disap- 
pear, or to be converted into the clear central space ; or, it 
may be, broken up and confounded in the more opaque con- 
tents. The number of spherules increases as the cell grows, 
and it is very soon apparent that the now very thick parietal 
deposit of cell contents is breaking up into small portions or 
lobular masses, the centre becoming clear, and apparently 
filled only with a clear aqueous fluid. When the cell has 
thus acquired a considerable size, the contents begin to un- 
