628 - Heredity and Evolution 



STENTOR 



STYLONYCHIA 



Fig. 32-4. Protozoa with cilia: Class Ciliophora. As adults, the Suctoria (e.g., 

 Podophrya) have tentacles instead of cilia. 



ganization generally occurs following con- 

 jugation, shortly after the zygote nucleus has 

 been formed. Or it may occur in a single 

 individual — either by autogamy or by endo- 

 mixis. Essentially these latter processes of 

 nuclear reorganization are similar, except 

 that autogamy involves a fusion of two mi- 

 cronuclei (within the same individual), 

 whereas endomixis does not involve any nu- 

 clear fusion. 



The nutrition of most Ciliata is holozoic, 

 but there are a few parasitic species. One 

 mild intestinal inflammation in man is 

 caused by a parasitic ciliate, Ballantidium 

 coli. However, this form occurs more fre- 

 quently in the intestine of the pig. 



The Suctoria. Among the Suctoria the off- 

 spring are produced by fission or by internal 

 budding; and only the young individuals are 

 active ciliated swimmers. Later each attaches 

 itself to the substratum by a stalk or disc, 

 loses its cilia, and develops tentacles (Fig. 

 32-4, Podophyra). Some of these tentacles 

 possess sticky knoblike tips, which hold the 



prey (usually some active ciliate), while 

 other sharply pointed tentacles pierce the 

 pellicle of the prey and conduct its cytoplasm 

 into a food vacuole within the suctorian. 



The Sporozoa. All Sporozoa are parasitic 

 and they are probably the most widely dis- 

 tributed of animal parasites. In fact, various 

 Sporozoa parasitize almost all other animals, 

 both Vertebrata and Invertebrata; and some 

 of the most devastating diseases of man and 

 other animals are caused by these unicellular 

 parasites. These diseases include the various 

 forms of malaria, in man; the coccidial dis- 

 eases of fowl; and the red-water fevers of 

 cattle. 



The malaria parasites all belong to the 

 genus Plasmodium, and like many parasites, 

 these Protozoa display a very complex life 

 cycle. This cycle (Fig. 30-7) includes two re- 

 productive stages, which take place while the 

 parasites are living in the mosquito, and a 

 third very active multiplication (sporulation), 

 which occurs in the blood stream of man and 

 other warm-blooded animals. 



