PHYLUM PROTOZOA 



the protoplasm of the living Radiolarian. Such an intimate 

 association between two living organisms is known as sym- 

 biosis. There can be no doubt that this association is bene- 

 ficial both to the Radiolarian and to the Alga. It is character- 

 istic of the plant-cell that under the action of light and in the 

 presence of the specially vegetable green colouring-matter, 

 chlorophyll, it is able to utilise for its nutrition the carbon 



B 



y mw/ 



nu-tfg 



FIG. ii. Collozoum inerme. A C, three forms of the entire colony, nat. size; 

 D, a small colony showing the numerous capsules (c. ca/>s.) and extra-capsular 

 protoplasm with vacuoles (vac.) ; K, spores containing crystals (c.) ; F, mega- 

 and microspore. (From Biitschli's Protozoa, after Hertwig and Brandt.) 



dioxide or "carbonic-acid gas" present in the air. The 

 carbon is seized and made use of by the plant-cell for the 

 building up of such compounds as starch and sugar, while 

 the oxygen is set free. The animal cell, on the other hand, 

 is continually using up oxygen and giving off carbon dioxide 

 in the process of respiration, while it is unable, in the 

 absence of chlorophyll, to manufacture such substances as 

 starch and sugar. Thus in this close association or sym- 

 Man. Zool. p 



