48 
Williamson on Volvox glohator. 
in the matured organism will be described immediately. When 
the gemma has attained its full size, by the process of segmenta- 
tion described in my former memoir, further changes occur. 
Translucent spaces separate the green protoplasms, now be- 
come hexagonal by mutual pressure. These translucent out- 
lines mark the development of the external cells investing the 
protoplasmic membranes. At first the two are in close oppo- 
sition ; they subsequently separate, as the cell increases in 
size, excepting at certain points where they remain in contact. 
Before tracing out the further stages of this process I must 
observe that the Volvox exhibits two apparently distinct states, 
which are, nevertheless, mere varieties of one species. In the 
one, each protoplasm assumes the appearance of fig. 1 Z>, being 
angular, and giving off thick, irregular and often dichotomous 
threads (1 c), the extremities of which are attached to the 
cell- wall (la). In this case, the radiating threads consist not 
only of the protoplasmic membrane, but also of its granular, 
mucilaginous contents. The other condition referred to is 
represented in fig. 10. Each protoplasm {10 d) is perfectly 
spherical, and connected with its neighbours by delicate capil- 
lary threads, these being so fine as to be sometimes almost 
invisible. In this state the cells to be described are often 
invisible ; nevertheless, they exist. 
The changes undergone by the stellate variety were described 
in my previous memoir. The cell expands, and as the pro- 
toplasm is only attached to it at certain points, the latter is 
drawn out until it finally assumes the stellate contour deli- 
neated in fig. I. Each of the radiating threads is attached to 
the cell-membrane by its peripheral extremity, at a point 
exactly opposite the corresponding threads of contiguous pro- 
toplasms. On rupturing a Volvox under water these threads 
become detached from the cell-wall, and passing through the 
stages represented in figs. 2 and 3, assumed that of fig. 4, 
which is precisely that of fig. 10, minus the connecting threads, 
a state which occasionally occurs in the living Volvox. 
In numerous examples of both these varieties of Volvox I 
found each protoplasm surrounded by an angular, usually 
hexagonal, areola, as represented in fig. 5 of my original me- 
moir. They appeared as dark outlines when the object was 
illuminated by transmitted light. On exposing these speci- 
mens for a while to the action of some re-agents, as glycerine, 
I soon found that each dark line was really double, and marked 
the boundaries of two cells. This was shown by the gradual 
separation of these cells at the angles of the areolae, as repre- 
sented in fig. 11, which is a faithful transcript of part of one 
of these specimens when mounted in glycerine. In this ex- 
