VII.] ANIMALS AND PLANTS. 157 



son's interesting investigations have shown, by a 

 disturbance of the electrical state of the contractile 

 substance, comparable to that which was found by Du 

 Bois Eeymond to be a concomitant of the activity of 

 ordinary muscle in animals. 



Again, I know of no test by which the reaction 

 of the leaves of the Sundew and of other plants to 

 stimuli, so fully and carefully studied by Mr. Darwin, 

 can be distinguished from those acts of contraction 

 following upon stimuli, which are called " reflex " in 

 animals. 



On each lobe of the bilobed leaf of Venus's fly trap 

 (Dioncea muscipula) are three delicate filaments which 

 stand out at right angle from the surface of the leaf. 

 Touch one of them with the end of a fine human hair 

 and the lobes of the leaf instantly close together * in 

 virtue of an act of contraction of part of their sub- 

 stance, just as the body of a snail contracts into its 

 shell when one of its " horns " is irritated. 



The reflex action of the snail is the result of the 

 presence of a nervous system in the animal. A mole- 

 cular change takes place in the nerve of the tentacle, 

 is propagated to the muscles by which the body is 

 retracted, and causing them to contract, the act of 

 retraction is brought about. Of course the similarity 

 of the acts does not necessarily involve the conclusion 

 that the mechanism by which they are effected is the 

 same ; but it suggests a suspicion of their identity 

 which needs careful testing. 



The results of recent inquiries into the structure of 



1 Darwin, " Insectivorous Plants," p. 289, 



