Chap. X.] TRANSMISSION OP MOTOR IMPULSE. 191 



Transmission of the Motor Impulse. In every case the 

 impulse from a gland has to travel for at least a short dis- 

 tance to the basal part of the tentacle, the upper part and the 

 gland itself being merely carried by the inflection of the 

 lower part. The impulse is thus always transmitted down 

 nearly the whole length of the pedicel. When the central 

 glands are stimulated, and the extreme marginal tentacles 

 become inflected, the impulse is transmitted across half the 

 diameter of the disc, and when the glands on one side of the 

 disc are stimulated, the impulse is transmitted across nearly 

 the whole width of the disc. A gland transmits its motor 

 impulse far more easily and quickly down its own tentacle 

 to the bending place than across the disc to neighbouring 

 tentacles. Thus a minute dose of a very weak solution of 

 ammonia, if given to one of the glands of the exterior ten- 

 tacles, causes it to bend and reach the centre; whereas a 

 large drop of the same solution, given to a score of glands 

 on the disc, will not cause through their combined influence 

 the least inflection of the exterior tentacles. Again, when a 

 bit of meat is placed on the gland of an exterior tentacle, 

 I have seen movement in ten seconds, and repeatedly within 

 a minute; but a much larger bit placed on several glands on 

 the disc does not cause the exterior tentacles to bend until 

 half an hour or even several hours have elapsed. 



The motor impulse spreads gradually on all sides from 

 one or more excited glands, so that the tentacles which stand 

 nearest are always first affected. Hence, when the glands 

 in the centre of the disc are excited, the extreme marginal 

 tentacles are the last inflected. But the glands on different 

 parts of the leaf transmit their motor power in a somewhat 

 different manner. If a bit of meat be placed on the long- 

 headed gland of a marginal tentacle, it quickly transmits 

 an impulse to its own bending portion ; but never, as far as 

 I have observed, to the adjoining tentacles ; for these are not 

 affected until the meat has been carried to the central glands, 

 which then radiate forth their conjoint impulse on all sides. 

 On four occasions leaves were prepared by removing some 

 days previously all the glands from the centre, so that these 

 could not be excited by the bits of meat brought to them by 

 the inflection of the marginal tentacles ; and now these mar- 

 ginal tentacles re-expand after a time without any other 



