MICROSCOPE AT THE POND-SIDE. 63 



regarded as a true plant. It consists of a large 

 number of spores, or cells, each having two cilia, 

 and connected together by a delicate network of 

 threads. In the interior of this moving sphere are 

 seen smaller globular masses, of a dark-green colour, 

 which are the young of the volvox, which have not 

 yet developed the network by means of which their 

 spores are separated, and their ciliated ends pre- 

 sented to the water, and by means of which their 

 movements are effected. 



Another form which is now regarded as a loco- 

 motive plant is the Euglena viridis, seen at figure 

 15, plate 1. It is often found in prodigious num- 

 bers, giving to water the appearance of green-pea 

 soup. When placed under the Microscope, it fre- 

 quently presents a red speck, or point, at one end, 

 and an elongated tail at the other. The red spot 

 has been regarded as an eye ; but if it is watched, 

 it will be found the red colour will often extend 

 from the red spot to the rest of the body ; and it 

 is probable that the red colour is only a change in 

 the condition of the chlorophyle contained in its 

 interior. Amongst this class of plants it is not 

 unfrequent for the chlorophyle to assume a red 

 colour at certain stages of its growth. 



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, 

 as seen at a, in figure 26, plate 2. Gradually the 

 cells of the filament 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- 



