] 5-4 THE MINUTE. 



that unsound, yet, for the time, when the microscope was 

 in far fewer hands than it is now, it contained much to 

 interest and much to instruct. The minutely invisible 

 world has now become tolerably familiar to most persons 

 of education; and thousands of eyes are almost constantly 

 gazing on the surprising forms of animals and plants, 

 which the microscope reveals. 



The study of one particular class of these organisms, 

 the Diatoms, has become quite a fashion, and the reunions 

 of our microscopists are almost exclusively occupied with 

 the names, the scientific arrangement, the forms and 

 sculpturings of these singular objects. I have already 

 had occasion to mention them in relation to the important 

 part they play in the economy of creation ; but it may not 

 be amiss to devote a few words more to them, with the 

 view to make the reader better acquainted with their 

 general appearance. 



A flat pill-box or cylindrical tin canister, which is much 

 wider than it is deep, will give a good idea of many of 

 the Diatoms, such as Arachnodiscus. The top and bot- 

 tom of the box are formed by flat circular glassy plates, 

 called valves, and the sides by a ring or hoop of similar 

 material. Sometimes the outline of the valves (with 

 which the hoop agrees) is oval, or oblong, or square, or 

 triangular, instead of circular ; and their surface is some- 

 times convex in various degrees, but the side is generally 

 upright, or in other words, the surface of the hoop passes 

 in a straight line from the edge of one valve, whatever its 

 outline, to that of the other. 



