50 



THE SMALLEST LIVING THINGS 



The two main subdivisions of this group are the fungi and the 

 algae, the latter having chlorophyll by which they are able to 

 create, with the energy of sunlight, the organic compounds of 

 their bodies from carbon dioxide, water, and salts. Fungi, how- 

 ever, have no chlorophyll and lack this power. 



According to the classification of West and Fritsch in British 

 Fresh-Water Algae, the algae are divided into eleven classes 



(see page 49). In the 

 majority of these classes 

 some minute living things 

 are to be found, but only 

 in a few of them are all 

 the types of microscopic 

 size. In practically all 

 these groups motile 

 stages alternate with qui- 

 escent phases. The mo- 

 tile phase for the most 

 part is characterized by 

 the presence of from one 

 to four vibratile flagella, 

 and the quiescent phase 

 by the loss of flagella 

 and by the secretion of 

 a jelly within which 

 the individuals are em- 



Fig. 20— HYDRURUS FOETIDUS 

 This organism has been called an animal. The bushy 

 growth, B, is made up of branches shown more highly- 

 magnified at A, where the yellow chlorophyll-holding 

 cells are embedded in a gelatinous matrix. From time bedded. In this quieSCent 

 to time swarm cells, C, are formed and swim away. 

 D and E, two views of a cyst formed by the organism, 

 A, C, D, and E, from Doflein after Klcbs; B, 

 from Pascher 



Magnifications : A, 150; C, D, and E, 800 

 B, 1/3 natural size 



phase, they may multiply 

 by repeated division un- 

 til large masses are 

 formed which are some- 

 times easily visible to the naked eye. This gelatinous, 

 so-called palmella phase does not occur in animal flagellates. 

 In some forms the motile phase is dominant {e.g., Euglenineae) , 

 in others the palmella phase from which at times flagellated 

 cells escape for a brief period of motile life, e.g., Hydrurus 

 (Fig. 20 ) ; 



Colonial forms likewise occur in nearly all groups. Colony 

 formation may be accompanied and brought about by the secre- 



