Williamson on Volvox glohator. 
55 
produced where they were attached to the protoplasm. As 
subsequent additions were made to their length, they would 
readily push through the apertures so left. After the cilia 
have fallen off, these apertures can occasionally be seen 
arranged in pairs, as described in my last memoir. I have, in 
my cabinet, one specimen in which two large Infusoriae have 
been developed within the Volvox, and have apparently eaten 
away many of the protoplasms without destroying the integrity 
of the sphere : the cilia have also fallen off : the remaining 
membranes confirm my previous description of the appearance 
and relative positions of these apertures. 
The fluid with which the sphere is filled is not mere water, 
but is apparently mucilage. In a preparation in which a 
number of these objects are mounted in dilute alcohol, this 
gummy matter has changed to a brown colour, and refused to 
mingle with the alcohol, as would be the case supposing it to 
be mucilaginous. This proves that it is a true secretion from 
the organism, and not merely water absorbed by endosmosis. 
We may possibly obtain from this source an explanation of 
the distension of the entire sphere, of the individual cells, and 
of the vesicles investing the germs. As this gummy secretion 
increased in quantity, each thin membrane investing the 
respective protoplasms from which the fluid was derived, would 
become distended for its reception, as the mere result of internal 
centrifugal pressure. The secretion itself is, perhaps, little 
more than a diluted condition of the same gum as that which 
is more or less completely converted into cellulose in the 
various investing membranes just enumerated. 
I cannot but think that the details now brought forward, 
resulting from a careful re-examination of the entire subject, 
will convince every unbiassed observer of the general accuracy 
of my previous conclusions, and especially those relating to the 
cellular structure of the walls of the sphere. In the memoir in 
which these conclusions were recorded, I pointed out the close 
analogy that existed between the development of Volvox and 
that of many of the lower Algae and Confervae. I also referred 
to the obvious resemblance of each protoplasm to the well- 
known Zoospores. 
It is only whilst the segmentation of the gemmae is in 
progress that a real relation exists between Volvox and young 
growing Confervae. At a later period every segment of the 
former becomes converted into a Zoospore : each Zoospore, 
in turn, having the power to cast off its cilia, and go through 
a new process of segmentation, in precisely the same way as 
the Zoospores of a Conferva or a Vaucheria. Only a few in 
each V^olvox are selected for this purpose, but the potentiality 
