No. 603] 



ECOLOGY OF THE PROTOZOA 



159 



Not only may the various stimuli arising from the dif- 

 ferent elements of the environment assort species into 

 communities, but the effects of these stimuli may not 

 always be the same. A given stimulus may at one time 

 produce a certain type of reaction, and at another time a 

 somewhat different type. This fact, also, experimentally 

 verified by Jennings, led him to suppose that something 

 analogous to, if not identical with true varying ''physio- 

 logical states" obtains in the Protozoan body. If this be 

 so then the problem of Protozoan ecology is still further 

 complicated, as far as any assignment of species to definite 

 fixed local environments is concerned. 



For collecting Protozoa and water samples the writer 

 has found the following useful : a small silk plankton net 

 (with draw string bottom) about six inches in diameter 

 and ten inches deep ; a glass or metal pipette, fully a foot 

 in length, operated by a compression bulb at one extrem- 

 ity, for sucking samples of light sediments from the bot- 

 toms of pools and streams; several small glass dipping 

 tubes ; a large table spoon ; a thermometer, and a plentiful 

 supply of variously sized water tight jars with screw 

 tops. With such an outfit as this the material described 

 in the following paper was secured. The samples were 

 examined immediately after being brought into the lab- 

 oratory, in order that the proportions of species might be 

 accurately recorded. 



From each sample ten slides were searched. The sig- 

 nificance of the terms few, numerous, rare, etc., is as fol- 

 lows: 



Over ten individuals of one species per slide abundant 



Average of 5-10 numerous 



Average of 2-5 several 



Average of .5-2 few 



Average of less than .5 rare 



The samples were taken from the uppermost layer of 

 silt on the bottoms of pools, streams, etc., the utmost care 

 being taken not to disturb the sediment below or to roil 

 the water. Upwards of fifty samples were secured repre- 

 senting five distinct environmental types. These five 

 types described are : 



