828 UTRICULARIA NEGLECTA. [Chap. XVIL 



to the air in the intercellular spaces. Bladders containing 

 dead and captured animals usually include bubbles of air, 

 but these cannot have been generated solely by the process 

 of decay, as I have often seen air in young, clean, and empty 

 bladders; and some old bladders with much decaying matter 

 had no bubbles. 



The real use of the bladders is to capture small aquatic 

 animals, and this they do on a large scale. In the first lot of 

 plants, which I received from the New Forest early in July, 

 a large proportion of the fully grown bladders contained 

 prey; in a second lot, received in the beginning of August, 

 most of the bladders were empty, but plants had been select- 

 ed which had grown in unusually pure water. In the first 

 lot, my son examined seventeen bladders, including prey of 

 some kind, and eight of these contained entomostracan crus- 

 taceans, three larva; of insects, 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 re- 

 mains, but not appearing very full, there were one, two, four, 

 two, and five crustaceans. A plant of Utricularia vulgariSf 

 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 Algte of 

 many kinds, Infusoria, and other low organisms, which evi- 

 dently lived as intruders. 



Animals enter the bladders by bending inwards the pos- 

 terior free edge of the valve, which from being highly elastic 

 shuts again instantly. As the e<lge 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 



