INrUS6RIA. 



139 



shallow that its microscopical contents may be more 

 readily captured, and it occupies less space than the 

 ordinary vessels offered by the dealers. I have 



been in the habit of selecting such jars as could 

 be bought for from ten to fifteen cents each, several 

 of which may be used at once for purposes of experi- 

 mentation, or for the cultivation of different classes of 

 microscopic animal and vegetable life. Such an aqua- 

 rium, if kept near a north window, will thrive all 

 winter, giving the microscopist a continuous supply of 

 interesting living objects, not necessarily confined to 

 Infusoria, but, if he wish, embracing many groups of 

 microscopic creatures. 



- If the vessel of pond water be left near the window 

 for a few days, the Infusoria will increase in a surprising 

 manner. But the bottle's contents should be exam- 

 ined immediately, for although many forms that will 

 not be in the gathering when first made will develop 

 there in a short time, others will die and melt away 

 almost as soon. The collection should therefore be 

 examined with the microscope as soon and as often as 

 possible,, for the peculiar rule is that certain animal 

 forms will abound and flourish for a while, seeming to 

 appear suddenly, only to vanish as suddenly to give 

 place to others of different form, character and habits. 

 The food supply acceptable to one kind may become 

 exhausted, and the environment agreeable and benefi- 

 cial to that form may become so changed that some 

 are killed either by starvation or by unpropitious sur- 

 roundings, while there may be present an abundance 

 of nutriment specially needed by the other kinds that 

 so speedily succeed those that have died; indeed, the 

 diffluent bodies of the latter may furnish the food de- 



