but not appearing very full, there were one, two, four, two, and five crustaceans.  A plant of Utricularia vulgaris, which had been kept in almost pure water, was placed by Cohn one evening into water swarming with crustaceans, and by the next morning most of the bladders contained these animals entrapped and swimming round and round their prisons.  They remained alive for several days; but at last perished, asphyxiated, as I suppose, by the oxygen in the water having been all consumed.  Freshwater worms were also found by Cohn in some bladders.  In all cases the bladders with decayed remains swarmed with living Algae of many kinds, Infusoria, and other low organisms, which evidently lived as intruders.

Animals enter the bladders by bending inwards the posterior free edge of the valve, which from being highly elastic shuts again instantly.  As the edge is extremely thin, and fits closely against the edge of the collar, both projecting into the bladder (see section, fig. 20), it would evidently be very difficult for any animal to get out when once imprisoned, and apparently they never do escape.  To show how closely the edge [page 406] fits, I may mention that my son found a Daphnia which had inserted one of its antennae into the slit, and it was thus held fast during a whole day.  On three or four occasions I have seen long narrow larvae, both dead and alive, wedged between the corner of 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