312 DARWINIANA. 



gland, not merely resting on the drop ; but the inflec- 

 tion is then much less pronounced and more tran- 

 sient. Even a bit of thin human hair, only -g-gVo" °^ 

 an inch in length, weighing only the T8 ^ 40 - of a 

 grain, and largely supported by the viscid secretion, 

 suffices to induce movement ; but, on the other hand, 

 one or two momentary, although rude, touches with a 

 hard object produce no effect, although a repeated 

 touch or the slightest pressure, such as that of a gnat's 

 foot, prolonged for a short time, causes bending. The 

 seat of the movement is wholly or nearly confined to 

 a portion of the lower part of the tentacle, above the 

 base, where local irritation produces not the slighest 

 effect. The movement takes place only in response 

 to some impression made upon its own gland at the 

 distant extremity, or upon other glands far more re- 

 mote. For if one of these members suffers irritation 

 the others sympathize with it. Yery noteworthy is 

 the correlation between the central tentacles, upon 

 which an insect is most likely to alight, and these ex- 

 ternal and larger ones, which, in proportion to their 

 distance from the centre, take the larger share in the 

 movement. The shorter central ones do not move at 

 all when a bit of meat, or a crushed fly, or a particle 

 of a salt of ammonia, or the like, is placed upon 

 them ; but they transmit their excitation across the 

 leaf to the surrounding tentacles on all sides ; and 

 they, although absolutely untouched, as they succes- 

 sively receive the mysterious impulse, bend strongly 

 inward, just as they do when their own glands are ex- 

 cited. Whenever a tentacle bends in obedience to an 

 impulse from its own gland, the movement is always 



