Chap. XVII,] MANNER OP CAPTURING PREY. 329 



the edge fits, I may mention that my son found a Daphnia 

 which had inserted one of its antennas 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 comer of the valve and collar, with half 

 their bodies within the bladder and half out. 



As I felt much diflSculty in understanding how such mi- 

 nute and weak animals, as are often captured, could force their 

 way into the bladders, I tried many experiments to ascertain 

 how this was affected. 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 

 80 as to project barely i of an inch, entered with some diffi- 

 culty; 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 dis- 

 appeared 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^ 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 long splinter, of which one end rested oblique- 

 ly 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 larvte, 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 t** of an 

 inch, .391 mm.) of green box-wood, which were just heavy 

 enough to sink in water, on three valves. These were exam- 

 ined after 19 hrs. 30 m., and were still lying on the valves; 



