the valve and collar, with half their bodies within the bladder and
half out.
As I felt much difficulty in understanding how such minute and weak
animals, as are often captured, could force their way into the
bladders, I tried many experiments to ascertain how this was effected.
The free margin of the valve bends so easily that no resistance is felt
when a needle or thin bristle is inserted. A thin human hair, fixed to
a handle, and cut off so as to project barely 1/4 of an inch, entered
with some difficulty; a longer piece yielded instead of entering. On
three occasions minute particles of blue glass (so as to be easily
distinguished) were placed on valves whilst under water; and on trying
gently to move them with a needle, they disappeared so suddenly that,
not seeing what had happened, I thought that I had flirted them off;
but on examining the bladders, they were found safely enclosed. The
same thing occurred to my son, who placed little cubes of green
box-wood (about 1/60 of an inch, .423 mm.) on some valves; and thrice
in the act of placing them on, or whilst gently moving them to another
spot, the valve suddenly opened and they were engulfed. He then placed
similar bits of wood on other valves, and moved them about for some
time, but they did not enter. Again, particles of blue glass were
placed by me on three valves, and extremely minute shavings of lead on
two other valves; after 1 or 2 hrs. none had entered, but in from 2 to
5 hrs. all five were enclosed. One of the particles of glass was a
[page 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 larv , that the
bladder was torn from the branch and shaken, and yet the splinter did
not fall out. My son also placed little cubes (about 1/65 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. 30 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
348