Chap. XVII. MANNER OF CArTUEING PREY. 405 



grown bladders contained prey ; in a second lot, re- 

 ceived in the beginning of August, most of the 

 bladders were empty, but plants had been selected 

 which had grown in unusually pure water. In the 

 first lot, my son examined seventeen bladders, in- 

 cluding prey of some kind, and eight of these con- 

 tained entomostracan crustaceans, three larvse of in- 

 sects, one being still alive, and six remnants of 

 animals so much decayed that their nature could not 

 be distinguished. I picked out five bladders which 

 seemed very full, and found in them four, five, eight, 

 and ten crustaceans, and in the fifth a single much 

 elongated larva. In five other bladders, selected from 

 containing remains, but not appearing very full, there 

 were one, two, four, two, and five crustaceans. A plant 

 of TJtricularia 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 w^ere 

 also found by Cohn in some bladders. In all cases 

 the bladders with decayed remains swarmed with 

 living Algse 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 



