44 
Busk on Volvox glohator. 
existence. At some periods not a single specimen from a 
given locality will exhibit it, whilst at another, every indi- 
vidual will show it at the first glance. Thus in the month of 
, August last, when, in a certain pond on Blackheath there was 
the most incredible abundance of Volvox^ so great in fact as to 
render the water at the lee side of the pond in certain spots 
of a deep green colour, and to cause it to afford, when collected, 
a very strong herbaceous or confervoid smell, the majority 
of the plants exhibited the stellate form of spores, or rapidly 
acquired spores of that character, and very many were in, or 
soon assumed, the form of V. aureus. They seemed in fact to 
be entering upon their hybernating state. Many among them, 
however, though all small and starved-looking, were of the 
common kind ; in all these Mr. Williamson's hexagonal areola- 
tion was very distinct. In the month of October, however, 
upon returning to the same pond, I was able to find very few 
Vblvoces at all, and all of the usual kind ; in none of these could 
I detect the least appearance of the same arrangement. I there- 
fore conclude that the greater or less distinctness, or complete 
absence of this character, is to be referred to external condi- 
tions with which we are not fully acquainted. The appear- 
ance itself I explain in this way. It appears to me that each 
zoospore is imbedded in a distinct gelatinous or semi-fluid 
envelope of considerable thickness, and that the hexagonal 
areas are formed by the sides of these distinct masses of gelati- 
nous matter coming into contact. I am inclined to think that 
there is no distinct membrane containing this gelatinous matter : 
if there be, it must be infinitely thin, because the line of con- 
tact is extremely delicate and single. I conceive, in fact, that 
each ciliated zoospore is surrounded with a gelatinous or 
semi-fluid areola, of the same nature precisely as that which 
surrounds the embryo Volvox while within the parent, and 
in which also it is not I think possible to detect a distinct 
limitary membrane. This envelope of the ciliated zoospores 
contains a nitrogenous element, which sometimes, on the addi- 
tion of iodine, gives rise to the appearance of minute heads 
around the outer periphery of each gelatinous mass, or in the 
lines of the hexagonal areas as seen in fig. 25. It is to be 
observed also, that connecting filaments of protoplasma may 
occasionally be seen to pass from one zoospore to another 
across the line of junction of the two gelatinous envelopes 
(fig. 24). These zoospores therefore of Volvox would appear 
to represent the " encysted zoospore " of Cohn (^Protococcus 
pluvialisy &c.), and his fig. 43, plate 67, may perhaps be 
taken as a fair representation of what I conceive to be the 
condition in these connected zoospores in Volvox. This ex- 
