TROPICAL AQUARIUM FISHES 141 
swim through the water. by means of circlets of hairs 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 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 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, 
Fic. 96. Common Forms or Microscopic ANIMAL LIFE IN FRESHWATER 
(Greatly magnified) 
1. Loxopes, a very common form. 
2. CERATIUM, a very common form, especially in ponds and lakes. 
3. PARAMAECIUM, a very common form, the slipper animalcule. 
4. Bursaria, a very common form, one of the largest. 
5. STYLONYCHA, a very common form, found everywhere. 
6. PHAcUS, not so common as the above numbers. 
7. SPIROSTOMUM, common everywhere. 
8. EucLena, common everywhere. 
9. CHILODON, common everywhere. 
10. TRACHELOCERCA, common everywhere, the swan animalcule. 
11. Evpototes, not an aquarium in America without examples. 
12. Dipin1um, predacous, feeds on paramaecium and others. 
13. TRACHELOCERCA, small but plentiful. 
14. Coteps, the barrel animalcule, common. 
