ticles slowly change their positions, and travel from one end to the other of the arms, but are commonly found near their bases.  They are present in the quadrifids of young bladders, when only about a third of their full size.  They do not resemble ordinary nuclei, but I believe that they are nuclei in a modified condition, for when absent, I could occasionally just distinguish in their places a delicate halo of matter, including a darker spot.  Moreover, the quadrifids of Utricularia montana contain rather larger and much [page 404] more regularly spherical, but otherwise similar, particles, which closely resemble the nuclei in the cells forming the walls of the bladders.  In the present case there were sometimes two, three, or even more, nearly similar particles within a single arm; but, as we shall hereafter see, the presence of more than one seemed always to be connected with the absorption of decayed matter.

The inner side of the collar (see the previous fig. 20) is covered with several crowded rows of processes, differing in no important respect from the quadrifids, except in bearing only two arms instead of four; they are, however, rather narrower and more delicate.  I shall call them the bifids.  They project into the bladder, and are directed towards its posterior end.  The quadrifid and bifid processes no doubt are homologous with the papillae on the outside of the bladder and of the leaves; and we shall see that they are developed from closely similar papillae.

The Uses of the several Parts.—­After the above long but necessary description of the parts, we will turn to their uses.  The bladders have been supposed by some authors to serve as floats; but branches which bore no bladders, and others from which they had been removed, floated perfectly, owing 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 [page 405] 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 larvae 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,