PROTOZOA AND THE UTRICLES OF UTRICULARIA. 251 



solutions, that it is doubtful whether any putrid fluid habitually 

 passes outward. But we must remember that a bladder generally 

 captures several animals, and that each time a fresh animal 

 enters, a puff of foul water must pass out and bathe the glands." 

 On the contrary, my experiments prove that when an animal 

 enters a bladder, medium is taken in rather than forced out, 

 and that fluid passes outwards between the time of one capture 

 and that of the next succeeding capture, i.e., during the period 

 of compression. Darwin's main conclusion may, therefore, be 

 correct, provided the glands around the entrance absorb material 

 if this is forced out of the valve during the compression of the 

 bladder. 



EXPERIMENTS WITH EUGLENAS. 



Euglenas are of frequent occurrence in the bladders of Utricularia 

 plants in nature. In 1922 euglenas were found to be present in 

 almost all of the bladders of Utricularia plants obtained from a 

 pond on the campus of the Johns Hopkins University and almost 

 every bladder was infected on plants that had been kept in a 

 dish in the laboratory for several months. The number present 

 in a single bladder as determined by counting those in ten bladders 

 selected at random, ranged from 8 to 510, with an average per 

 bladder of 215 (Hegner, 1923). The pond from which these 

 plants were taken contains large numbers of euglenas at certain 

 times of the year and these bladders may have become infected 

 with these free-living specimens. It was believed, however, at 

 that time, that the Utricularia bladders contained digestive 

 ferments and on this account might successfully withstand the 

 conditions within the digestive tract of tadpoles in which euglenas 

 had been proved to be normal inhabitants (Hegner, 1923, 

 \Yenrich, 1923). When fed to tadpoles, however, these euglenas 

 were promptly digested. Euglenas were also noted in many of 

 the bladders on plants of Utricularia vulgaris var. americana 

 collected near Bar Harbor, Me., although not in as great numbers 

 as in those on plants collected in Baltimore. 



Utricularia bladders lose their infection with euglenas when 

 kept for a long period in the laboratory. Bladders of Utricularia 

 were used for experimental purposes in the spring of 1925 that 

 were taken from plants that had been kept in large stender 



