130 MICROSCOPE IN AQUARIUM WORK 



disport themselves through the water. In fact, rotifers derive their name 

 from the wheel-like appearance produced by the motion of the circlets of 

 cilia while feeding and swimming. For culture water to have practical 

 food value a single drop should contain at least half a dozen living 

 animals that can be seen in the manner suggested. Water rich in life 

 will show rotifers so thickly that they almost touch one another— prob- 

 ably two hundred in a small drop. In taking water from the culture 

 tank to feed the fish it should be skimmed from the surface or the 

 animals extracted from the water by a plankton net, which is nothing 

 more than a small net of the finest bolting cloth. 



Besides the examination of water for living food there are many 

 other interesting possibilities for the microscope in aquarium work. Dis- 

 eases, the development of eggs, plant structure, algae, the structure of 

 daphnia, cy clops and other crustacean foods are a few of the subjects 

 which may be taken up with profitable interest. 



A study of the microscopic world within the aquarium will prove a 

 most fascinating pursuit. An instrument equipped with a 16 m.m. 

 (2-3 inch) objective and a high- and a low-power eyepiece will show 

 everything needed, giving satisfactory magnification. 



Those wishing to explore this field further will find the following 

 works to be helpful: "Aquatic Microscopy for Beginners," by Stokes; 

 "Marvels of Pond Life," by Slack; "Evenings at the Microscope," by 

 Gosse. 



