Cmar. XVII.] MANNER OF CAPTURING PREY. oat 
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 selected 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 crustaceans, three 
larvæ 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 remains, 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 con- 
sumed, Freshwater worms were also found by Cohn in some 
bladders. In all cases the bladders with decayed remains 
swarmed with living Alge of many kinds, Infusoria, and 
other low organisms, which evidently 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 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 fits, I may mention that my son found a Daphnia which 
had inserted one of its antennæ into the slit, and it was thus 
held fast during a whole day. On three or four occasions I 
have seen long narrow larve, 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 
