Cuar. XVII] MANNER OF CAPTURING PREY. 329 
colloid substances. or instance, particles of glass were 
placed on various points of narrow strips of moistened gela- 
tine, and these yielded and became bent with extreme slow- 
ness. 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. ‘lo 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 movement of small 
crustaceans, but the valve did not open. Some bladders, 
before being brushed, were left for a time in water at tem- 
peratures between 80° and 130° F. (26°-6—54°:4 Cent.), as, 
judging from a wide-spread analogy, this would have ren- 
dered them more sensitive to irritation, or would by itself 
have excited movement; but no effect was produced. We 
may therefore conclude that animals enter merely by forcing 
their way through the slit-like orifice; their heads serving 
asa wedge. But I am surprised that such small and weak 
creatures as are often captured (for instance, the nauplius of 
a crustacean, and a tardigrade) should be strong enough to 
act in this manner, seeing that it was difficult to push in one 
end of a bit of hair + of an inch in length. Nevertheless, 
it is certain that weak and small creatures do enter, and 
Mrs. ‘Treat, of New Jersey, has been more successful than any 
other observer, and has often witnessed in the case of 
Utriculria clandestina the whole process.* She saw a tardi- 
grade slowly walking round a bladder, as if reconnoitring ; 
at last it crawled into the depression where the valve lies, 
and then easily entered. She also witnessed the entrapment 
of various minute crustaceans. Cypris “was quite wary, 
“but nevertheless was often caught. Coming to the entrance 
“of a bladder, it would sometimes pause a moment, and then 
“dash away ; at other times it would come close up, and even 
“venture part of the way into the entrance and back out as 
“if afraid. Another, more heedless, would open the door 
“and walk in; but it was no sooner in than it manifested 
“alarm, drew in its feet and antenne, and closed its shell.” 
Larve, apparently of gnats, when “feeding near the en- 
“trance, are pretty certain to run their heads into the net, 
“‘whence there is no retreat. A large larva is sometimes 
* «New York Tribune,’ reprinted in the ‘Gard. Chron.’ 1875, p. 303, 
