394 ELEMENTARY BIOLOGY. [CHAP. 



less cell-wall, surrounding the protoplasm, 

 but separated from it by a clear space. 

 Note in various specimens — The two cilia 

 prolonged from the protoplasm through aper- 

 tures in the cell-wall; their motionless part 

 within the wall; their vibratile portion out- 

 side it. The colourless thin external layer 

 of the protoplasm collected into a little heap 

 at the point from whence the cilia arise. 

 The delicate colourless processes radiating 

 from the outer protoplasmic layer to the in- 

 terior of the cell-wall. The colour — usually 

 green, but frequently one bright red spot is 

 present. 



Here, as in the vegetative stage, the colour- 

 ing matter is limited to the relatively large 

 chromatophores, and here also a nucleus is 

 present. 



/?. Cells of smaller size but much like the above 

 if the cellulose sac were removed, and the 

 radiating processes extending to it from the 

 protoplasm withdrawn. These are the micro- 

 zoospores. 



b. Try to find specimens in which the movements 

 are becoming sluggish, and see the cilia in 

 motion. 



c. Stain with iodine ; this kills the cells, and stops 

 their movements, and frequently renders the 

 cilia very distinct. 



d. Try to find zoospores which have come to rest, 

 and are beginning to form a new cell-wall. 



