SOME COMMON OBJECTS 57 



little creatures must have a drop or so of water in 

 which to move, and be covered with a thin cover- 

 glass. We examine them with a 1-inch or ^-inch 

 objective. Now it can be seen that each globe 

 consists of a sphere of united ceUs, and that from 

 each ceU two lashes project. The lashes of all the 

 cells, acting in vmison, propel the globe in its aquatic 

 revolutions. But the sphere also encloses other 

 smaller globes, miniature editions of itself, and if 

 the parent sphere be burst, the enclosed ones are 

 set free, and behave like their parents. In fact, 

 the parent spheres do burst in the natural course 

 of things, and set their young free to grow and 

 repeat the story. This is the method of reproduction. 

 Some observers declare that these globes are 

 animals ; others claim them as vegetable ; and the 

 latter are in the majority. 



It behoves me to refer to another variety of 

 vegetable Ufe common in the pond and other 

 situations, having considerable power of move- 

 ment : I mean the Diatoms. They may be found in 

 great numbers forming a green or reddish scum on 

 mud or pond bottoms, and even in old cart ruts in 

 which water has stood for some time ; they are also 

 found attached to seaweeds, and in numerous other 

 places. When pond-hunting, the student should 

 secure scrapings from the surface of the mud. 

 Such scrapings are almost sure to contain diatoms. 

 A minute portion of the material gathered placed 

 on a glass sHp in a very httle water is sufficient for 

 examination at one time. Diatoms are minute, 

 one-celled plants enclosed in a sheU of flinty material 

 known as the " cell waU." The shell is two-valved, 



8 



