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number of minute liole3 arranged in a symmetrical manner (con- 
stituting the so-called secondary markings), which differs in every 
species 1 have observed. Fig. 3 shows a portion of such a capping 
of one of them. 
The cell-walls connecting the two surfaces are exceedingly thin 
and fragile, and are easily destroyed and lost sight of, while the two 
plates which they join are comparatively stout, and are ifften found 
separate and entire. The details of cell-form vary widely in different 
species. 
In the case of the larger Pinnulariw, e. g. viridis and nobilis, it 
cm be easily seen that the striae are pseudo-tubes contained in the 
walls of the valve, and which may be considered as formed by the 
lapping towards one another of the edges of a groove sculptured on 
the inner wall of the valve. I have observed indications of channels 
of communication between these pseudo-tubes and the outside of 
the valve, similar to those forming the secondary markings of the 
Coscinodiscs, but seek further confirmation. Fig. 4 shows a partly 
charged valve of Pinnularia major (?). 
Of “ dotted ” diatoms, Cocconema lanceolatnm (fig. 5), Stauroneis 
fhoenicenteron (fig. 6), and the various Pleurosigmse and Naviculse , 
all that can be affirmed with certainty is that the dots are hollows. 
Further experiment is required to determine the point whether they 
have or have not the same cellular structure as the Coscinodiscs. 
Mr. Smith has shown that they have two skins or layers ; is it not 
probable that these are connected in the same manner as those of the 
larger forms ? Edge views of fragments of charged Cocconema and 
Stauroneis seem to show the black sulphide extending as a streak 
from one face to the other of the single valve, but in the case of such 
exceedingly minute structure, as is here in question, it is very easy to 
be misled by one’s prepossessions, and it is therefore quite possible 
that on this point I have been deceived. What precise function these 
lacunae or pores fulfil in the economy of the organism, is a question 
which I hope to study in the immediate future. 
