DIATOMS 223 
king in his stronghold. When in repose, or alarmed, 
the animal contracts into the space within the tube, 
but when feeding it expands its body, which opens 
out about the mouth like the petals of a flower. 
Each petal-like “ process ”’ is surrounded with cilia, 
or fine hairs, which move and create a vortex in 
true Rotifer fashion. Unless the habits of this 
animal were commonly observed and the facts con- 
stantly verified, we could hardly imagine or credit 
such a tiny creature being endowed with such con- 
structive ability. 
The time is passing only too rapidly, but we have 
yet to examine some Diatoms which I had the 
fortune to get amongst the mud I gathered in this 
tube. We are piling wonder upon wonder. Did 
you ever see such a remarkable object as that which 
is now gliding about under the microscope? Ah! 
there are several of them, all of the same species. 
They travel like tiny ships, and can reverse their 
engines more rapidly than can be done in any boat. 
Our specimens are Navicula (i.e., little ships). They 
are very, very small, and need to be magnified 
greatly in order that we may see their details. 
Now, what are Diatoms? Are they plants or 
animals ? Seeing that they move about so easily, 
I suppose you would vote them animals. But, in 
reality, they are plants. They are unicellular, or 
one-celled organisms ; the brownish colouring matter 
you see in them is allied to the colouring substance 
of ordinary leaves, known as “chlorophyll.” The 
living substance of the Diatom is enclosed in a kind 
of shell of flinty material, which is known as the “cell- 
wall.” This shell is of two valves, which are as a 
