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 movement 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 130° F. (26°.6-54°.4 Cent.), as, judging from a wide- [page 408] spread analogy, this would have rendered 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 as a 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 a hair 1/4 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 Utricularia clandestina the whole process.* She saw a tardigrade 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 antennæ, and closed its shell.” Larvæ, apparently of gnats, when “feeding near the entrance, are pretty certain to run their heads into the net, whence there is no retreat. A large larva is sometimes three or four hours in being swallowed, the process bringing to * ‘New York Tribune,’ reprinted in the ‘Gard. Chron.’ 1875, p. 303. [page 409] mind what I have witnessed when a small snake makes a large frog its victim.” But as the valve does not appear to be in the least irritable, the slow swallowing process must be the effect of the onward movement of the larva.