238 MICROSCOPE IN AQUARIUM WORK 



or cilia arising from the front of their heads, by the vibratile action 

 of which they swim and disport themselves through the water. In 

 fact, rotifers derive their name from the wheel-like appearance pro- 

 duced by the motion of the circlets of cilia while feeding and swim- 

 ming. For culture water to have practical food value a single drop 

 should contain at least half a dozen living objects that can be seen 

 in the manner suggested. Water rich in life will show rotifers so 

 thickly that they almost touch one another — probably 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. 

 Diseases, the development of eggs, plant structure, algse, the structure 

 of daphnia, cyclops and other crustacean foods are a few of the sub- 

 jects 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 a little further will find the 

 following works to be helpful : "Aquatic Microscopy for Beginners," 

 by Stokes ; "Marvels of Pond Life," by Slack ; "Evenings at the Micro- 

 scope," by Gosse. 



