378 GENERAL BIOLOGY 



in rain water spouts, and in stone urns, that are alternately 

 drenched with showers and baked in the sun. With every 

 sun-baking, they are almost completely dessicated, and 

 become contracted and wrinkled into almost unrecogniz- 

 able shapes; but with the next shower they "soak up" again, 

 and resume normal activity. 



Study 46. Observations on the dessication and resuscita- 

 tion of rotifers. 



Materials needed : An abundance of living rotifers, pref- 

 erably of the genus Philodina, which is commonly found in 

 the dried crust of the bottom in stone urns in cemeteries, etc. , 

 and which may be cultivated in little porcelain dishes with 

 rain water in the laboratory. For convenience of handling, 

 cultures are best made on squares of fine-meshed filter paper 

 laid in the hollow of the bottom of the dishes. For methods 

 of handling, of concentrating, of isolating the rotifers see 

 appendix. 



The student should obtain specimens at one laboratory 

 period, should isolate some of them in the bottom of a hol- 

 low ground slide in the hollow of a piece of filter paper fitted 

 thereto, should set this slide away uncovered to dry by 

 evaporation, and at the next laboratory period, should 

 examine the rotifers dry, and then should cover them with 

 water and watch them resuscitate. 



The record of this study should consist of notes on and 

 sketches of the things observed. 



j. Local distribution of animals. 



That food and shelter are the primary factors determining 

 the distribution of animals is almost too obvious to be 

 stated. Where to find a living and establish a home is the 

 great question confronting every animal even man. 

 Terrestrial plants live where they must ; but most animals 



