THE MANIFESTATIONS OF LIFE 67 



Loeb points out that certain Holothurians tend to 

 creep vertically upward when placed upon a plane 

 surface. If the plane be slowly turned so that the 

 position is inverted, the animal remains quiet until 

 accommodated to the new order, and then again be- 

 gins to creep upward. This is an example of negative 

 geotropism. 



Among the higher animals the disposition to assume 

 definite positions with relation to gravitation is even 

 more pronounced. The mechanism by which it is 

 accomplished is complicated, being partly voluntary 

 and partly reflex, and accomplished through visual 

 and tactile impressions, as well as through the semicircu- 

 lar canals of the internal ear which are supposed to be 

 equilibrating organs. 



Inversion of the higher animals, or the forced assump- 

 tion of any abnormal position, is followed by intense 

 anxiety to resume the normal, but so many factors co- 

 operate to produce the effects that it becomes extremely 

 difficult to determine in how far they are geotropic 

 in character. 



CONDUCTIVITY. 



By conductivity is meant the conduction or trans- 

 mission of any stimulus from the part immediately 

 irritated or stimulated to others more or less remote. 



Conductivity is almost as widely distributed a property 

 of living substance as is the irritability upon which it 

 depends. 



As irritability was difficult to determine in the absence 

 of immediate response, so it is only possible to deter- 

 mine the extent of conduction in cases in which it leads 

 to visible effects. 



In the behavior of the plasmodia of the slime moulds 

 we find evidences that the effect of stimulation is exerted 

 upon the whole, not upon that particular portion stimu- 

 lated. Thus, there must be transmission of the stimu- 



