THE MINUTE. 



endochrome, the nature of which is not very 

 clearly ascertained. The single specimen, includ- 

 ing the two valves and the hoop, with their con- 

 tents, is called a frustule. 



The manner in which these beautiful, but most 

 minute atoms increase, is highly curious. The 

 pill-box-like frustule becomes deeper by the widen- 

 ing of the hoop, thus pushing the valves further 

 from each other; then across the middle two 

 membranes form, which, by and by, from the 

 deposition of flinty matter, become glassy valves, 

 corresponding to the two outer valves, and then 

 the whole frustule separates between these two 

 new valves, and forms two frustules. The old 

 hoop (in some cases at least) falls off, or allows 

 the hoops of the new-made frustules to slip out of 

 it, like the inner tubes out of a telescope. 



Now, the separation of the frustules thus made 

 is not always so complete, but that they remain 

 adherent to one another, by some point of con- 

 tact ; and hence arises a most singular and inter- 

 esting appearance often presented by these bodies. 

 Let us suppose that the original frustule was of 

 the shape of a brick, and that by successive acts 

 of self-division, it has formed itself into a number, 

 say a dozen of bricks. These, of course, are laid 

 one on another, forming a pile; but all the indi- 

 viduals adhere to one another by a minute point 

 at one corner, and the matter of adherence is 

 sufficiently tenacious and sufficiently yielding to 

 allow of the brick-shaped frustules moving freely 

 apart in every point, except just the connecting 

 angle. It is not the same corner that adheres all 

 up the pile; more frequently opposite corners alter- 

 nate with each other, yet not very regularly, and 

 thus an angularly jointed chain of the little bodies 

 is formed, which is very characteristic. In some 

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