ioo BEHAVIOR OF THE LOWER ORGANISMS 



and hence remain outside (Jennings, 1899 c, p. 373). While in a cer- 

 tain case individuals from one culture were repelled by^g- per cent lithium 

 chloride, those from another culture were found to be quite indifferent 

 to a solution of the same chemical sixteen times as strong, swimming 

 readily into a drop of J- per cent lithium chloride (Jennings, 1899 c, 

 p. 374). When placed in a vertical tube, Paramecia from certain cul- 

 tures gather at the top; from other cultures at the bottom; while in 

 other cases they remain scattered throughout the tube (Sosnowski, 

 1899). Corresponding variations are found in the reaction to water 

 currents. Similar differences are to be observed with regard to the 

 positive contact reaction (Putter, 1900, p. 253). Infusoria in certain 

 cultures are strongly inclined to attach themselves to solids, forming 

 dense masses on the surface; in other cultures such masses are never 

 formed. In fresh cultures the animals are usually much inclined to 

 attach themselves in this way ; in old cultures they are not. Even in 

 a culture where most of the animals attach themselves, there are always 

 a number of specimens which remain persistently free. Variations are 

 to be observed at times in the reactions to electricity (Jennings, 1904 h). 

 One sometimes observes that while most of the specimens in a prepara- 

 tion are reacting to the electric current in a precise way, a few speci- 

 mens do not react at all, swimming about at random. Sometimes 

 single specimens will be seen swimming toward the anode, while all the 

 rest swim toward the cathode. This is most often observed after the 

 current has been reversed several times. 



Whether the variations mentioned in the last paragraph are due to 

 changes which have occurred during the life-time of the animals, or 

 whether they are permanent differences between different individuals 

 we do not know. In either case they are of importance, since they give 

 much opportunity for the action of natural selection. This is a point 

 to which we shall return later. 



We know, however, that sometimes the behavior of the same indi- 

 vidual varies, and in some cases we can form an idea of the nature of 

 the change which has occurred. If a Paramecium is subjected to a 

 strong induction shock, it fails for some time thereafter to react to weak 

 shocks, though at the beginning it reacted to these (Statkewitsch, 1903). 

 This result is probably due to a change in the animal such as we com- 

 monly call fatigue. To be explained possibly in a similar way is the 

 following occasional observation. A specimen in the continuous elec- 

 tric current is swimming toward the cathode ; on reversal of the current 

 it retains its orientation and continues to swim forward, — now of 

 course toward the anode. This lasts usually but a short time. 



Paramecia which have been living at the usual temperatures show 



