io MINUTE MARVELS OF NATURE 



not all ; one side of the shell or frustule becomes 

 slightly larger than the other, and fits over the 

 smaller, after the manner of the halves of a pill- 

 box or canister. 



On the surfaces of these flinty shields deli- 

 cately carved and chased symmetrical markings 



Fig. 4. An arranged group of the cleaned shells, or 

 shields, of the tiny plants called " diatoms." The 

 actual group measures ^ of an inch in diameter 



are revealed when considerably magnified. An 

 arranged group of these tiny and wonderful 

 shields is shown in Fig. 4. 



As this group measures only one-twelfth of an 

 inch in diameter, it will be understood that the 

 shields are considerably magnified, although but 



