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, 



Fig. 96. 



Common Forms of Microscopic Amm.\l Life in Freshwater 

 (Greatly magnified) 



1. LoxoDES, 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. Stylonvcha, a very common form, found everywhere. 



6. Phacus, not so common as the above numbers. 



7. Spirostomum, common everywhere. 



8. Euglena, common everywhere. 



9. Chilodon, common everywhere. 



10. Trachelocerca, common everywhere, the swan animalcule. 



11. EupoLOTEs, not an aquarium in America without examples. 



12. DiDiNiUM, predacous, feeds on paramaecium and others. 



13. Trachelocerca, small but plentiful. 



14. CoLEPs, the barrel animalcule, common. 



