CHAP. XVII MANNER OF CAPTUEING PREY. 409 



" mind what I have witnessed when a small snake 

 '' makes a large frog its victim." But as the valve 

 does not appear to be in the least irritable, the 

 slow swallowing process must be the effect of the 

 onward movement of the larva. 



It is difficult to conjecture what can attract so many 

 creatures, animal- and vegetable-feeding crustaceans, 

 worms, tardigrades, and various larvse, to enter the 

 bladders. Mrs. Treat says that the larvae just 

 referred to are vegetable-feeders, and seem to have a 

 special liking for the long bristles round the valve, but 

 this taste will not account for the entrance of animal- 

 feeding crustaceans. Perhaps small aquatic animals 

 habitually try to enter every small crevice, like that 

 between the valve and collar, in search of food or pro 

 tection. It is not probable that the remarkable trans- 

 parency of the valve is an accidental circumstance, 

 and the spot of light thus formed may serve as a 

 guide. The long bristles round the entrance ap- 

 parently serve for the same purpose. I believe that 

 this is the case, because the bladders of some epi- 

 phytic and marsh species of Utricularia which live 

 embedded either in entangled vegetation or in mud, 

 have no bristles round the entrance, and these under 

 such conditions would be of no service as a guide. 

 Nevertheless, with these epiphytic and marsh species, 

 two pairs of bristles project from the surface of the 

 valve, as in the aquatic species ; and their use pro- 

 bably is to prevent too large animals from trying to 

 force an entrance into the bladder, thus rupturing the 

 orifice. 



As under favourable circumstances most of the blad- 

 ders succeed in securing prey, in one case as many as 

 ten crustaceans ; as the valve is so well fitted to 



