164: ANIMALS AND PLANTS. 



son's interesting investigations have shown, by a dis- 

 turbance of the electrical state of the contractile sub- 

 stance, comparable to that which was found by Du Bois 

 Reymond to be a concomitant of the activity of ordi- 

 nary 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 Yenus'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 molec- 

 ular change takes place in the nerve of the tentacle, 

 is propagated to the muscles by -which the body is re- 

 tracted, and causing them to contract, the act of retrac- 

 tion 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 care- 

 ful testing. 



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



