282 S. O. MAST AND K. S. LASHLEY 



given opportunity to 'try' the various different conditions supplied by 

 the neighboring environment. Paramecium does not passively wait 

 for the environment to act upon it, as Amoeba may be said, in com- 

 parison, to do. On the contrary, it actively intervenes, determining 

 for itself what portion of the environment shall act upon it, and in 

 what part of its body it shall be primarily affected by the varying con- 

 ditions of the surrounding water. By thus receiving samples of the 

 environment for a certain distance in advance, it is enabled to react 

 with reference to any new condition which it is approaching, before it 

 has actually entered these conditions. 



Several years ago, in making observations under the binocu- 

 lar on paramecia in rather large quantities of solution contain- 

 ing numerous particles in suspension, the senior author was 

 surprised to find no evidence whatever of a movement of par- 

 ticles toward individuals which were swimming freely. As seen 

 under the binocular with a magnification of 40 to 60 diameters, 

 there is, under such conditions, no appreciable movement of the 

 particles either in front of or along the sides of the paramecia. 

 If pronounced water currents were drawn in continuously from 

 in front of the animals, as is maintained by Jennings, one would 

 expect, with numerous paramecia swimming about in every di- 

 rection, to find the liquid about them churned into violent motion, 

 but this is not the case; quite the contrary; the liquid under such 

 conditions appears to be stationary. The paramecia, gliding 

 about among the particles in suspension disturb them surpris- 

 ingly little. 



These contentions are supported by the results of more exten- 

 sive observations by the junior author. Most of these obser- 

 vations were made on Paramecium but some were also made on 

 other organisms. 



OBSERVATIONS ON PARAMECIUM 



The ciliary currents produced by free-swimming paramecia 

 were studied first in a watch glass containing approximately 1 

 cc. of fluid, consisting usually of a dilute suspension of India ink 

 in fresh culture fluid to which the animals had become accli- 

 mated. Under these conditions most careful observations both 

 under a binocular and under a compound microscope failed to 



