DIATOMS 



as there are thousands of kinds of diatoms, so there 

 are thousands of shapes assumed by their respective 

 boxes. Some are round like a pill-box, some are 

 triangular, others are boat-shaped ; while some have 



Fi - 35- Heliopelta. Enlarged several hundred diameters. 



four corners, others have seven, and so on. All are 

 marvellously decorated. To purchasers of micro- 

 scopes they are of immense service, in that their fine 

 lines are tests and guides as to the power and accuracy 

 of the instruments from which they are selecting. 



