HEREDITY AND VARIATIONS IN PROTOZOA 



567 



is increased by the fact that comparatively few life histories of 

 Protozoa are known. INIany variations that have been recorded 

 may be cyclical in nature and repeated in all life histories of indi- 

 \idnals of the species. These correspond to differentiations in 

 ontogeny of Metazoa and have been more fully discussed in Chapter 

 X. The fact that such variations breed true by cell division is to 

 be expected for the organism could not do otherwise. The test 

 comes with amphimixis or parthenogenesis. 



310 



OOJOPOOHHM 



45 



Fig. 234. — Size variations in eight families of Paramecium. (After Jennings.) 



A. Uniparental Inheritance. —It is quite possible that changes in 

 the genot\'pe or organization of Protozoa may occur and remain 

 permanently, and such changes may be due to environmental or 

 to internal causes. Changes due to environmental causes, to be 

 permanent, would ha^'e to so affect the germinal make-up that 

 reversions would not occur. Thus individuals formed by reversions 

 from the double Uroleptus described in Chapter X (p. 465) never 

 regenerated the double organism but lived as single individuals of 

 Uroleptus mobilis (Series 91 of Table, p. 560). Here the organi- 



