JOINTED FRUSTULES. 159 



not always so complete, but that they may remain ad- 

 herent to one another by some point of contact ; and 

 hence arises a most singular and interesting appear- 

 ance often presented by these bodies. Let us suppose 

 that the original frustule was of the shape of a brick, 

 (for the pill-box form is only one of many), 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 individuals adhere to one another by a 

 minute point at one corner, and the matter of adhesion 

 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 alternate 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 species, in which the form is 

 a lengthened oblong, the frustules have the faculty of 

 sliding partially over each other ; and thus the chain 

 takes the form of a series of steps, of which the length 

 is much greater than the width or height. 



Some of the forms have the frustule seated at the 

 end of a long and slender footstalk, a thread of spun 

 glass, on whose elastic summit they wave and dance 

 with every movement of the waters. The self-division 

 of the frustules here frequently extends to the stalk ; 

 and so we find beautiful little fan-like tufts or shrubs, 

 all educed by this imperfect multiplication. In almost 



