RALPS, ON DIATOMACES. 15 
it is filled with a yellowish, granular mass, mixed with 
numerous colourless vesicles.” Subsequently, the presence 
of these internal cells has been, in two instances (Meridion 
Zinckent and Himantidium Soleirolit), adopted as part of the 
specific character. In this conclusion I could not concur, 
because I found in the same filament such frustules inter- 
spersed with others in the common state. More recently, in 
Professor Smith’s beautiful work on the British Diatomaceze, 
we have had his opinion respecting this condition of Meridien 
circulare thus stated : 
“Tn var 6. we meet with a curious modification in the 
growth of the frustule, which has been regarded by some 
observers as characteristic of a distinct species. re 
A close examination of such frustules, especially in the living 
state, has led me to the conclusion that the appearance of a 
double wall of silex is owimg to the formation within the 
original frustule of a second perfect cell, instead of the usual 
mode of division by which the original frustule is divided 
into two half-new cells. In the present case, the central 
vesicle, or cytoblast, becomes enlarged without division, and 
secretes on its extension two new valves, which are pushed 
outwards until they lie in close approximation with the 
original valves. ‘This process is not always repeated, the 
usual mode of self-division again recurs, and two valves are 
formed in the interior of this new cell according to the nor- 
mal method. This unusual method of development is not, 
however, sufficiently constant to warrant the separation of 
such frustules from the species in which it occurs, perhaps 
hardly sufficient to constitute a variety, as frustules in both 
the ordinary and abnormal states may be met with in the 
same gathering, and even in the same filament.” 
As part of the above explanation seems to me inconsistent 
with what I have observed, I am anxious briefly to state my 
own views, and to solicit a re-examination of the phenomena 
by Professor Smith himself, satisfied that it would either 
induce him to modify his opinions, or by the discovery of 
new facts dissipate the uncertainty which at present may 
reasonably be entertained of the nature of these internal 
cells. 
Although it is true that “we frequently find in the same 
filament cells thus formed, and others following the normal 
mode of growth,” as I formerly showed, yet I cannot agree 
to Professor Smith’s statement under Himantidium Soleirolii, 
that “there is no doubt of its being merely an accidental 
modification of cell-growth.” On the contrary, I believe it 
to be a reproductive state of the species, and consequently to 
have a definite and important part in their economy. 
