Cuav. XVI MANNER OF CAPTURING PREY. 407 
long splinter, of which one end rested obliquely on 
the valve, and after a few hours it was found fixed, half 
within the bladder and half projecting out, with the 
edge of the valve fitting closely all round, except at 
one angle, where a small open space was left. It was 
so firmly fixed, like the above mentioned larve, that 
the bladder was torn from the branch and shaken, and 
yet the splinter did not fall out. My son also placed 
little cubes (abont j!; of an inch, ‘391 mm.) of green 
box-wood, which were just heavy enough to sink in 
water, on’ three valves. These were examined after 
19 hrs. 30 m., and were still lying on the valves; but 
after 22 hrs. 830 m. one was found enclosed. I may 
here mention that I found in a bladder on a naturally 
growing plant a grain of sand, and in another bladder 
three grains; these must have fallen by some accident 
on the valves, and then entered like the particles 
of glass. : , 
The slow bending of the valve from the weight of 
particles of glass and even of box-wood, though largely 
supported by the water, is, I suppose, analogous to the 
slow bending of colloid substances. For instance, 
particles of glass were placed on various points of 
narrow strips of moistened gelatine, and these yielded 
and became bent with extreme slowness. It is much 
more difficult to understand how gently moving a 
particle from one part of a valve to another causes it 
suddenly to open. To ascertain whether the valves 
were endowed with irritability, the surfaces of several 
were scratched with a needle or brushed with a fine 
camel-hair brush, so as to imitate the crawling move- 
ment of small crustaceans, but the valve did not 
open. Some bladders, before being brushed, were left 
for a time in water at temperatures between 80° and 
180° F. (26°6—54°-4 Cent.), as, judging from a wide- 
27 
