MESOTENIUM, AND SPIROTANIA. 219 
varying phases of its development, and say that, because 
such differ, that form is of no value. The phases of growth 
should be taken, and the comparison made, at the same point 
in development ; for very varied phases may certainly inter- 
vene, nor does this latter fact seem to me to conflict with my 
view. ‘The zygospore of Peniuwm Mooreanum figured on the 
plate referred to, or indeed that of any other Desmid or 
Conjugate, or that exceptional phase of Mesotznium, or the 
oospore of an Cidogonium, or even the zoospore of a Clado- 
phora or of a Drapernaldia, &c., are not more unlike, after 
all, to their parent or mature forms than an acorn is unlike 
an oak. 
Dr. Hicks further writes—“ The varying forms of their 
divisions show that their form changes very strangely. This 
is observable in almost every Conferva, and the Desmidieze 
are good examples.” Ido not quite comprehend this. Ifa 
cell of a Conferva or a Desmid during division is not actually 
of the same figure as one fully grown, surely it attains it when 
the process is completed. If he means that a Conferva or a 
Desmid during the act of division is able to change directly 
from one form to another, I hold that this is wrong, and that 
there is no foundation for such an assumption. Nay, “the 
varying forms of their divisions” seem rather in themselves 
to afford more or less useful characters. 
To pass on briefly to consider the communication from 
Dr. Wallich which I have just had the honour to read to the 
Society (vide infra), he, while contending for the greater or 
less instability of the Protophyta, the Desmidiez included, 
does not, however, make such a demand as that just adverted 
to. I shall, as the opportunity here occurs, venture to add 
a word or two in allusion to Dr. Wallich’s communication, 
referring mainly, as it does, to certain Desmidian forms. I 
have, indeed, ere now endeavoured to express my own views 
as fully as I could on this point; therefore I shall not here 
attempt to dilate at any length on the subject, as it would be 
but repetition. 
In the first place, then, Dr. Wallich alludes to my urging 
the persistence of type in the Desmidiacez, because they are 
more or less constant in a given locality. On the other 
hand, he urges that, unless these characters are found to 
occur under every variety of conditions, he cannot accept 
them as evidence of the persistence of type for which I have 
contended. Now, it seems, at first sight, that it is asking 
somewhat too much to demand that every variety of con- 
ditions should produce no effect, when it is only under 
certain conditions that some forms are found at all. But he 
