Closterium Ehrenbergii. 3 
delicate mucus is secreted around the approximated fronds ; these 
remove to a little distance from each other, undergo “ self-divi- 
sion,” and present altogether an irregular oval figure, the outline 
of which is formed by the periphery of the mucus, the four divi- 
sions of the fronds being placed in the middle in a somewhat 
quadrilateral manner (fig. 3). During the progress of self-divi- 
sion the internal membrane of the cell-wall becomes enlarged 
at the suture or line of separation, and projects in the form of 
an irregular cone with a blunt or rounded apex forming a beak, 
whose side view presents a triangular outline. This beak be- 
comes filled with endochrome, either by the dilatation or increase 
of the contents of the half-frond, and the divided frond assumes 
the appearance of one with two unequal segments, being what 
M. Morren calls “ une Closterie & deux cones inégaux ” (fig. 3). 
On these membranous expansions, at the concave surfaces of the 
fronds and close to the original sutures, there appear, almost 
simultaneously with the formation of the beaks, two circular 
projections, which rupturing at their apices, give egress to the 
delicate sacs which inclose the endochrome, and which drawing 
with them their contents and meeting with the endochrome-sacs 
emitted through similar projections from the other half-fronds, 
form by their connection irregular masses which quickly conso- 
lidate and assume the appearance of perfectly circular, smooth 
dark-coloured balls, the sporangia of Ralfs and seminules of 
Morren (figs. 4, 5). 
The discharge of the endochrome and formation of the spo- 
rangia are accomplished with much rapidity, and may often be 
seen taking place in the field of the microscope, the whole ope- 
ration not occupying more than a few minutes. It will be seen 
from an inspection of the figures, that during the formation of 
the sporangia there appears to be a second development of mu- 
cus in the form of rings around the reproductive bodies ; this 1s 
probably only the effect of the pressure produced by the growth 
of the sporangia on the mass of investing mucus. It will also 
be seen that the pale transverse band adopted by Ralts as a cha- 
racter of the genus Closterium, and which in figs. 1 and 2 occu- 
pies the centre of the undivided frond, is, upon self-division 
taking place, removed a little towards the extremities of the half- 
fronds (fig. 8). The reason as well as the cause of this motion 
{ am unable to explain, but it seems to confirm the propriety of 
adopting the band itself as a permanent and important cha- 
racter. 
With regard to the subsequent changes which take place in 
the sporangia, the time which elapses before they produce young 
fronds, and the mode in which such evolution of a fresh race is 
accomplished, I have not been fortunate enough to ascertain any- 
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