242 R. W. HEGNER. 



jecting mass of cells. This valve can open only inward. A 

 view looking down upon the mouth opening is shown in Fig. 3. 

 This view reveals two pairs of bristles projecting from the valve 

 near the lower edge, a row of glandular hairs near by, and 

 numerous glandular hairs attached to the valve near its upper 

 edge. Extending out into the vestibule from the side walls are 

 many glandular hairs of various lengths. The bladders vary in 

 size from about I mm. to 4 mm. in length. They are usually 

 filled with liquid but may contain bubbles of gas. They were 

 once thought to be floats which kept the plant near the surface 

 of the water, but the presence of small animals within them soon 

 placed them among the "insectivorous" plants. A typical 

 bladder when "set" and ready to function as a trap for the 

 capture of minute aquatic animals is laterally compressed as 

 shown in Fig. 4. Just after the capture of an organism the 

 bladder is much distended as indicated in Fig. 5. Darwin (1875) 

 noted that the bladders varied much in thickness according to 

 the quantity of water contained in them and that they "are 

 always somewhat compressed," but as will be explained later 

 he did not realize the significance of the compressed and expanded 

 conditions. 



The remarkable ability of these bladders to capture free- 

 swimming aquatic organisms is well indicated by an examination 

 of a typical branch. The branch studied consisted of a main 

 stem no cm. long bearing 4 side branches the combined length 

 of which was 110 cm. The number of bladders per cm. on the 

 main stem was estimated as 90, and on the side branches, as 36. 

 The total approximate number of bladders was therefore 13,860. 

 The organisms within 10 mature bladders selected at random 

 were counted. These consisted of entomostraca, insect larvte, 

 rotifers, usually euglenas and often other protozoa. Ento- 

 mostraca represented the principal article of food; these ranged 

 from 6 to 22 per bladder with an average of 12. A conservative 

 estimate of the number per bladder would be 10, which would 

 place the total number of entomostraca captured by this part 

 of the plant at about 150,000. The bladders live for some time 

 and as the victims die and break down fresh specimens are 

 captured, so that the total number captured by the plant during 



