Busk on Volvox glohator. 
37 
zoospore, when viewed from above, exhibits two highly refrac- 
tive spots placed side by side, which seem to represent the 
insertions or origins of the two vibratile cilia. 
The periphery of the cell presents a clear line, and appears 
to be formed of a delicate membrane — although, in the earlier 
stages of the existence of the zoospore, that is, before the for- 
mation of the eye-spot, or disappearance of the contractile 
vacuole, the whole evidently consists of a homogeneous sub- 
stance, in which the above described parts are imbedded. 
From the periphery of the zoospore proceed six thread-like 
processes, connecting it with as many of its neighbours. These 
threads appear to be simply continuations of the quasi cell- 
wall, and to be of the same nature chemically as it, as are also 
the vibratile cilia. The connecting threads are sometimes 
double, or even triple, between some one or more of the sur- 
rounding cells, and they are invariably continuous between the 
two cells. 
This description applies more particularly to the zoospores 
in situ. When the Volvox is ruptured, many appear to be- 
come immediately detached, and to be washed out, as it were, 
with the aqueous contents of the parent cell. Under these 
circumstances they lose some of their previous regularity of 
form, but not much ; they become more globular and the 
beak less prominent, but in other respects they appear much 
the same as before. The two vibratile cilia remain in An- 
nexion with them, and continue their active movements. This 
is opposed to Mr. Williamson's statement, that " when thus 
liberated they exhibit no traces of the two cilia, or probos- 
cides" of Ehrenberg, and agrees with that of the latter. 
Among the thus liberated ciliated zoospores will usually be 
found numerous detached cilia, which, as is observed by Mr. 
Williamson, are generally more or less coiled at one end into a 
ring. And besides these I have not unfrequently noticed some 
extremely delicate annular bodies, about 1 -9000th of an inch 
in diameter, perfectly clear and colourless, which seem as if 
they had escaped from the interior of the ruptured zoospore : 
but of this and their true nature I am unable to speak posi- 
tively. 
Having thus described what I conceive to be the anatomy of 
the common form of Volvox glohator^ I will thus sum up the 
result of what my observations have led me to conclude as to 
its structure. 
1. That it originates in an apparently nucleated, discoid 
cell, which is generated in the interior of the parent, and 
liberated in a perfect, though not fully matured form ; within 
which are contained similar germs. 
