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. 



13. 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 protoplasm withdrawn.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. 



