REVOLVING PLANTS. 51 



Now, if a number of these volvoces be placed in a 

 glass jar, they will sink to the bottom when in 

 darkness, but in the light will all arise and con- 

 gregate together against the side where there is 

 most light. Place the jar in the sunlight and they 

 will move to, and revolve rapidly on, the bright 

 side. The motion of these bodies thus appears to 

 be due to a combination of causes the globular 

 form, the vibratile cilia, and the sun. 



The cilia here referred to is a matter of great 

 interest, and worthy of attentive study. Let us 

 try to understand it. Looking now at one of those 

 globes under slight pressure, so as to keep it in 

 one place, and with a high magnifying power, we 

 see that the entire surface of the sphere is covered 

 with a network of cells, each cell being hexagonal 

 (produced by mutual pressure) in form, and each 

 one attached to its neighbour by a very fine thread 

 which runs straight across from cell to cell. The 

 attachment is not at the angles, or by the sides of 

 the hexagons, but by the delicate threads which cross 

 the interspaces between. The whole membrane of 

 the globe is thus seen to be so many distinct cells, 

 held together by this thread-like attachment. As 

 E 2 



