6 
Transactions of the 
[ATonthly Microscopical 
Journal, July 1, 1869. 
valve. Hence, in scientific descriptions, the terms " striation and 
lineation " are no longer admissible, and the books we now have in 
our hands are not a mirror held up to nature, in which the members 
of this family could recognize themselves, for "strise and lines" 
are just as little applicable to the rows of hemispheres on the 
surface of a diatom-valve as they would be to a hayfield with its 
rows of haycocks. 
Further, with reference to structure, a vertical section of 
P. Quadratum reveals the fact that the siliceous hemispheres on 
the outer surfaces have corresponding hemispheres on the inner 
surfaces ; in fact, we have perfect spheres of silica set eqnatorially 
in the siliceous tissue of the valve.' That such arrangement is the 
law of the structure, does not admit of doubt. The silica is the solid 
material round which the carbonaceous portion of the living cell 
gathers, and thus it has its counterpart in every cell of every plant 
in the vegetable kingdom, for the varying solid material of the cells 
of plants is as necessary as the carbonaceous material for enabling 
them to perform their proper functions in the economy of vegeta- 
tion. In this respect it may be said to correspond with the osseous 
system in animals. As a very different arrangement of the same 
solid materials is invariably found in the mineral kingdom, we 
cannot but recognize the action of different laws in the formation 
of the crystal and of the cell ; for, if the soluble silica obeyed the 
same law during its solidification in the latter case as in the former, 
we should have examples of rock-crystal in the cell instead of a 
siliceous cell-wall. This consideration ought to be borne in mind 
when we treat of the important subject of cell-formation. Proto- 
plasm alone is not to Nature's liking. 
As I was a pupil, I may almost say a friend, of Ehrenberg, who 
named for me the Xanthidia which I found in flint, I have been 
for a long time unable to recognize the entire validity of the argu- 
ments which exclude the Diatomaceae from the animal kingdom. 
But when I now see the form and arrangement of the silica on the 
cell-wall of the diatom to be so exactly like its form — and its arrange- 
ment in consecutive corpuscles — on the stomata of many plants 
that I have examined, and so exceedingly unlike any secretion of 
silica in any other kingdom than the vegetable, I find no difficulty 
whatever in placing the Diatomaceae among the unicellular algae. 
On viewing the surface of different diatom-valves, we find a 
great difference in the diameter of the hemispheres, and in their 
distance from each other. We are told, popularly, and in suffi- 
ciently vague language, so far as structure is concerned, that the 
"striw" range between about 30 and 100 in yoWth of an inch, 
and, to adduce an example, that the striae of P. strigilis are much 
closer than those of P. formosum — a statement which gives no 
idea of the fact that the diameters of their hemispheres are the 
