100 LIVERPOOL BIOLOGICAL SOCIETY. 
about with a creeping motion, then come to rest, and 
develop into new individuals (fig. 4). In the remaining 
families of filiform Cyanophyces, power of spontaneous 
movement is confined to these hormogones; the Oscillaria- 
ces, on the other hand, derive their name from the 
peculiar oscillating movement of the entire filament; but 
according to Borzi, one of the most careful observers of 
these forms of life, the power of motion is limited to the 
reproductive period. 
We now turn to a group of Aleze much higher in deve- 
lopment, the Desmidiaceze. Desmids have two modes of 
multiplication, a sexual process of conjugation, and a non- 
sexual mode of propagation by division. It is the pheno- 
mena connected with the latter to which I wish to direct 
your attention ; and we may take as an example a species 
of the familiar genus Stawrastrum (fig. 5). When division 
is about to commence, the endochrome retreats slightly 
from the band or ‘ isthmus,” which connects the two half- 
cells with one another, and the two halves then separate, 
retaining their connection only by a narrow band formed by 
the gradual broadening of the isthmus ; this isthmus is after 
a time divided into two by a transverse septum midway 
between the two half-cells, and parallel to the constriction 
between them. The endochrome now passes out of each 
original half-cell into the half of the band in connection 
with it ; and at the same time the half-band bulges, and, 
growing rapidly, assumes the form and appearance of an 
original half-cell. Fresh formation of chlorophyll is at the 
same time taking place in it, and the half-band becomes a 
complete half-cell. The whole of these processes have 
taken place in the course of a few hours, or even less; and 
we have now two individuals attached to one another, and 
frequently remaining in connection for a considerable 
period, until at length they separate. In the spiny species 
