Williamson on Volvox globator. bl 
plasm connecting it with the peripheral walls of its cell. 
Such a section however cannot be obtained until chemical 
re-agents have rendered the tissues rigid, which process alters 
their arrangement and aspects. 
The entire thickness of the cellular peripheral wall of the 
Volvox is about 1-1 400th of an inch, in specimens that have 
been a few days mounted in glycerine. The superficial dia- 
meter of the cells in the living Volvox varies from 1 -800th to 
1-lOOOth of an inch. 
The next question relates to the nature of the threads that 
connect together the protoplasms of the two varieties of 
Volvox. These cannot be exactly the same in figs. 1 and 10. In 
fig. 1 , the entire protoplasmic mass is drawn out into a stellate 
form. Each thread consists of the protoplasmic membrane, 
and a portion of its contents. In fig. 10, on the other hand, the 
threads contain little or none of the protoplasmic granules, 
but appear to consist solely of a portion of the membrane. 
Of course to produce such a result this membrane must be highly 
ductile, and consequently but partially organized. That the 
threads are ductile and capable of being drawn out is easily 
seen on compressing a Volvox between two glasses. The fluid 
distending the sphere is very viscid and probably consists of 
mucilage. This must have been secreted by the protoplasms. 
When we remember that cellulose is but a modified form of 
gum, we can readily conceive that the conversion of the one 
into the other may sometimes be imperfectly accomplished 
amongst these lower forms of vegetation. Such I believe 
to be the explanation of the ductility of the protoplasmic 
membrane, and of the threads into which it is drawn out. 
Fig. 16 throws a little additional light on this subject. We 
see from it that whilst the thread sometimes consists of the 
drawn-out membrane (16 a), at others the membrane has re- 
ceded from the outer cell-wall, leaving only a very faint line, 
thickened at its peripheral extremity, marking the former 
point of junction with the outer cell-wall. The same thing is 
seen in fig. 7. In both these examples the threads were ori- 
ginally of the stellate type seen in fig. 1. Whilst the points of 
contact with the outer cell- wall are still indicated, they have 
lost their irregular dichotomous character, and are reduced 
to straight, radiating, capillary threads, such as are seen in 
fig. 1. The greater portion of the viscid membrane has receded 
towards the protoplasm, whilst a small part has in like manner 
accumulated at the point of attachment to the cell-wall, form- 
ing the peripheral dots seen in the above figures ; similar 
appearances present themselves in the other variety, fig. 10. 
Near the centre of fig. 11, the threads uniting several of the 
