THE ANIMAL IN THE WORLD 



535 



Here must also be mentioned some special kinds of metabolism which 

 Soec differ greatly, though not in principle, from the pro- 



Metabolisms cesses we have just traced. Certain organisms, such 

 as the yeast fungus and many bacteria, are able to live 

 without free oxygen, although they contain no chlorophyll to enable 



Fig. 392. — Euglena viridis. 

 A t A\ A", Three positions of the body. 



them to obtain it by the splitting of carbon dioxide. Such organisms 

 are called anaerobic. They obtain their energy by the decomposition 

 of oxygen-bearing molecules of organic substances, as we have seen 

 some parasitic animals to do (p. 309). Thus the minute fungi 



Fig. 393. — Hamatococcus ( = Sfharella) pluvialis, a minute, green, 

 flagellate organism, with plant-like (holophytic) nutrition, found 

 in standing rain-water. 



A, Ordinary phase ; B, products of asexual reproduction which takes place within 

 a cyst by fission repeated to form four young ; C, conjugation : 16-32 gametes 

 are formed by repeated fission. 



chp.i flask-shaped chloroplast, underlying the surface of the body except at the 

 front end ; cu., cellulose shell or cuticle, standing off from the body ; opposite 

 etc. stands the red eyespot (there is usually a good deal more red pigment in the 

 body) ; fl., fiagellum ; ««., nucleus ; pr., protoplasmic processes running to 

 shell ; pyr--, pyrenoid, surrounded by starch granules. 



of which yeast consists decompose grape sugar into alcohol and carbon 

 dioxide according to the equation 



C 6 H 12 6 =2C 2 H 6 + 2C0 2 , 



with the evolution of so much energy in the form of heat that the 

 temperature of the surrounding solution rises. This is the process of 



