22 



SYSTEMATIC ZOOLOGY 



on the surface. Respiration is effected internally by means of 

 the oxygen contained in the water in the food vacuoles, and 

 externally by the whole superficial surface of the body which 

 is in contact with the water. The products of katabolism, i.e. of 

 the breaking clou n of the protoplasm, the excretory products 

 proper, are believed to pass off through the contractile vacuole 

 (Fig. 2), when this is present, otherwise there is no definite 

 point of expulsion. 



Fig. 2. Amoeba polypodia in succi n ; the dark 



spot surrounded by a light ring is the nucleus; the light spot is the 

 contractile vacuole. (After F. F. Schulze, from Parker and Has- 

 well's Manual.) 



The processes of reproduction are not well known in all 

 the Rhizopoda. Simple division has been observed in all 

 the orders (Fig. 2); the nucleus divides bv direct or in- 

 direct division, and then the protoplasm divides. If there is a 

 contractile vacuole, it remains in one of the two individuals pro- 

 duced, and a new one forms in the other; if there are two con- 

 tractile vacuoles, one goes to each individual. Typical budding 

 also occurs, the new Rhizopoda being smaller than the older 

 or parent individual. Finally, spore formation attending en- 



