44 A HALF-HOUR WITH THE 



The transition from the filamentous to the mem- 

 branous form of these plants is well seen in the 

 species of Ulva. These are found in both fresh and 

 sea water. In the early stages of its growth, the 

 ulva presents the filamentous form of a conferva 

 (Fig. 24, a, PI. 2). Gradually the cells of the fila- 

 ment split up into two or three seams (b) ; and 

 this goes on till at last a broad flat membrane is 

 produced (c). 



If the plants of our fresh waters are interesting, 

 not less so are the animalcules ; for, just as we 

 have one-celled plants so we have one-celled ani- 

 mals, and it was only by the aid of the Microscope 

 that they were discovered and can be examined. 

 Wherever the above plants are found, there will 

 also be discovered animals to feed upon them. The 

 animal is distinguished from the plant by its feed- 

 ing on plants, whilst the latter feed on inorganic 

 substances. 



There is considerable difficulty in at once dis- 

 tinguishing between the lowest forms of animals 

 and plants. Although the animal generally pos- 

 sesses a mouth, and a stomach in which to digest 

 its vegetable food, there are some forms of animal 

 life so simple as not to possess either of these 

 organs. In the sediment from ponds and rivers 

 there will frequently be found small irregular 

 masses of living, moving matter. If these are 

 watched, they will be found to move about and 

 change their form constantly. As they press 

 themselves slowly along, small portions of vege- 

 table matter, or occasionally a diatom, mix, appa- 

 rently, with their substance. Cells are produced 

 in their interior, which bud off from the parent, 

 and lead the same life. These creatures are called 

 arnsebas (Fig. 16, PI. 1) ; and though they have no 

 mouth or stomach, they are referred to the animal 



