Protozoa 



89 



only with the highest inugnifieations. Their protoplasm is in a col- 

 loidal state and contains chromatic or nuclear substance, generally 

 forming nuclei readily distinguishable from the protoplasmic body, 



rf?5 



o 







Fig. 42. Different h'pes of soil algae (from Bristol). 



which is either naked at the surface or enclosed by a cell membrane. 

 Usually one or two nuclei are present; in some cases, several. Con- 

 tractile \acuoles, when present, are for the elimination of waste 

 fluids or possibly for the adjustment of the osmotic pressure of the 

 protoplasm. Some Mastigophora contain in their endoplasm green, 

 yellow, or brown chromatophores. The most important constituents 

 of the cell are the complex proteins, particularly the nucleins and 



