238 
PROCEEDINGS OE SOCIETIES. 
confervoids generally, that is, protoplasm coloured green by chlorophyll, 
and entirely enclosed in a “ primordial utricle,” which organ appears 
more evident as a real and distinct utricle than in any other vegetable 
cells I have seen. The contents of the cells often contain starch gra¬ 
nules. A circulation of their fluid contents has been noticed in 
various species; in Closterium and Penium, &c., it is of a very re¬ 
markable character. In Cosmarium Ralfsii ( Breb .), after the contents 
had lost their characteristic somewhat radiate appearance, and had be¬ 
come broken-up, I have seen a regular current rotating somewhat rapidly 
round-and-round the internal margin of each segment, and carrying the 
chlorophyll granules with it, very strikingly like that in Anacharis, &c. 
The ordinary mode of multiplication of the individual cells is by re¬ 
peated transverse division, which is effected by the interposition of new 
growth between the original segments, the older segments remaining 
unaltered, except (when they remain for some time attached) by being 
pushed asunder by the enlarging young segments. The exact manner 
in which this takes place differs slightly in detail in the different ge¬ 
nera. In Closterium, which in the various species is more or less of an 
arcuate or lunate form, the original cell acquires a constricted appear¬ 
ance at the middle; a separation of the endochrome having taken place, 
the new constriction gradually becomes deeper, until at length it is 
complete, when ultimate somewhat sudden separation is effected by a 
from-side-to-side sawing motion of the segments, which is highly cu¬ 
rious-to observe; the blunt convex new end of each now separated 
individual cell afterwards grows out, till the symmetrical more or less 
attenuated arcuate form of the frond is restored. Although I have 
not witnessed it in Penium digitus, I am greatly inclined to think 
that the mode described in Closterium holds good in this species. In 
Penium Brebissonii, although it doubtless follows the same rule as the 
other Desmids, the mode of increase can hardly be distinguished, and 
some botanists have included that species amongst the Palmellaceous 
Algae; but its central pale space and elongate form easily distinguish 
it. In such bipartite forms as Micrasterias, Euastrum, Cosmarium, Stau- 
rastrum, &c., to produce two exactly similar fronds from one, it is 
obvious that two new segments must be formed; but in these the growth 
of the new segments takes place, always to some, and often to a consi¬ 
derable, extent before their separation. The constricted portion of the 
old frond expands by the formation of a connecting tube, “ of which the 
interposed new coat is the direct continuation of that which lines the 
internal surface of the cracked halves of the old shell” (Hofmeister),*' 
and which is soon dilated into two globular or roundish enlargements. 
These are the rudiments of the two new segments, which soon increase 
in size, and in doing so push asunder the two older segments, acquire 
colour, and ultimately assume a like appearance, with all the characte¬ 
ristic lobes, sinuosities, or processes of the species, similar to those pos- 
* Translated in “Annals of Nat. Hist.,” third series, vol. i., No. 1, January, 1858. 
