Chap. II.] INFLECTION DIRECTLY CAUSED. 27 



with the glands. But as it was sometimes difficult, owing 

 to the refraction of the secretion, to feel sure whether the 

 particles were in contact, I tried the following experiment. 

 Unusually minute particles of glass, hair, and cork were 

 gently placed on the drops round several glands, and very 

 few of the tentacles moved. Those which were not affected 

 were left for about half an hour, and the particles were then 

 disturbed or tilted up several times with a fine needle under 

 the microscope, the glands not being touched. And now in 

 the course of a few minutes almost all the hitherto motion- 

 less tentacles began to move; and this, no doubt, was caused 

 by one end or some prominence of the particles having come 

 into contact with the surface of the glands. But, as the 

 particles were unusually minute, the movement was small. 



Lastly, some dark blue glass pounded into fine splinters 

 was used, in order that the points of the particles might be 

 better distinguished when immersed in the secretion; and 

 thirteen such particles were placed in contact with the de- 

 pending and therefore thicker part of the drops round so 

 many glands. Five of the tentacles began moving after an 

 interval of a few minutes, and in these cases I clearly saw 

 that the particles touched the lower surface of the gland. A 

 sixth tentacle moved after 1 hr. 45 m., and the particle was 

 now in contact with the gland, which was not the case at 

 first. So it was with the seventh tentacle, but its movement 

 did not begin until 3 hrs. 45 m. had elapsed. The remaining 

 six tentacles never moved as long as they were observed ; -and 

 the particles apparently never came into contact with the 

 surfaces of the glands. 



From these experiments we learn that particles not con- 

 taining soluble matter, when placed on glands, often cause 

 the tentacles to begin bending in the course of from one to 

 five minutes; and that in such cases the particles have been 

 from the first in contact with the surfaces of the glands. 

 When the tentacles do not begin moving for a much longer 

 time, namely, from half an hour to three or four hours, the 

 particles have been slowly brought into contact with the 

 glands either by the secretion being absorbed by the particles 

 or by its gradual spreading over them, together with its con- 

 sequent quicker evaporation. When the tentacles do not 

 move at all, the particles have never come into contact with 



