76 
Lauder^ on Marine Diatomaceos. 
spherical mass, witli a strongly defined outline. The de- 
fined outline gradually disappears ; the mass of endochrome 
becomes paler in colour ; a clear space is formed in its 
centre; the connecting hoop of the frustule at the same 
time increasing in breadth, until it equals the original length 
of the cell. The endochrome divides into two equal por- 
tions; a line of demarkation is formed in the connecting 
hoop, from which new awns begin to sprout, and thus two 
frustules are enclosed within the enlarged connecting zone; 
each composed of a new and an old A^alve. 
At certain seasons, or at certain ages of the fronds, this 
process takes a different direction. The condensed endo- 
chrome, instead of becoming paler and dividing, gradually 
assumes another shape, varying with the species, and secretes 
a siliceous envelope. In some species it becomes a body, 
with a capitate head and constricted neck at one end, and at 
the other end merely curved, and a broad connecting zone 
between them (PI. VIII, fig. 4, a, b : «, filament ; h, side 
view of sporangium). 
In other species the neck is wanting; some have the 
sporangium smooth, others bristly. Finally, the endochrome 
forms roundish, highly refractive globules within the Gonio- 
thecium-like body ; the filaments become very fragile, break- 
ing up on slight disturbance, and set free the enclosed 
bodies. The contents of the sporangium soon escape, but I 
have not been able to follow out the further processes they 
undergo towards the reproduction of a Chsetoceros. 
These bodies have hitherto been placed in a distinct genus 
of Diatomacece, viz., Goniothecium, although Mr. Brightwell 
has already shown that some of them at least were con- 
nected with Chsetoceros. I imagine that they are sporangia, 
formed by the conjugation, as it were, of the two valves of a 
frustule. It is rarely that all the frustules of a filament are in 
this sporangial state, some having these bodies enclosed, whilst 
other cells are undergoing the ordinary process of division. 
I am inclined tc believe that many, if not all the species in 
Goniothecium, Oniflalotheca, Hercothea, and perhaps in 
Dicladia, Periptera, and Syndenbrium, may, when found in 
the living state, turn out to be the sporangial bodies of species 
of Chsetoceros. 
Those figured in fig. 2, d, are very like Ehrenberg^s 
figure of Hercotlieca mcmiillaris ; the circumference of the 
connecting hoop being set round with minute setae, or a 
striated portion of the hoop projects beyond the valve. 
It is often difficult to distinguish species from varieties, as 
the awns seem to vary much in size, length, and stoutness. 
