PHYLUM PROTOZOA 27 



Budding (Fig. 13) differs from fission chiefly in the relative 

 sizes of the resulting parts. In fission, two or more approxi- 

 mately equivalent parts result from the partition of one individ- 

 ual. Through budding, on the other hand, the identity of a 

 parent organism is retained, for the buds arise as smaller out- 

 growths from the body of the producing individual. 



Conjugation in the Protozoa involves either the temporary or 

 permanent fusion of two or more individuals of the same species. 

 A simple type is found in the fusion of the cytoplasm of a number 

 of individuals to form a Plasmodium, as in the Mycetozoa. More 

 frequently the nuclei are involved in either a permanent fusion 

 resulting in true fertilization or a temporary fusion involving an 

 exchange of nuclear material. 



Endomixis. — An intricate process of nuclear reconstruction 

 without the fusion of individuals occurs in some Protozoa. 

 Details of this phenomenon, which is termed endomixis, have 

 been observed especially in Paramecium by Doctors L. L. Wood- 

 ruff and Rhoda Erdmann. They found that in Paramecium the 

 macronucleus gives off budlike fragments at regular time inter- 

 vals and that these fragments are absorbed in the cytoplasm. 

 While the macronucleus is being broken up, the micronucleus 

 undergoes a series of divisions, differing in detail in the different 

 species but resulting in the formation of eight products. In 

 Paramecium caudatum, which has a single micronucleus, a series 

 of three divisions produces the eight micronuclear bodies; while 

 in P. aurelia, which has two micronuclei, only two divisions of 

 the micronuclei occur. Part of the eight micronuclear bodies 

 disintegrate while of the remainder some form micronuclei, others 

 macronuclei. Thus wholly new nuclear equipment is formed 

 from a portion of a micronucleus after a manner strikingly similar 

 to the nuclear reorganization following conjugation. In Para- 

 mecium caudatum, endomixis occurs at regular intervals of about 

 60 days, while in Paramecium aurelia the period is approximately 

 30 days. 



In some other ciliates endomixis has been observed but in 

 these it usually occurs during an inactive period of encyst ment. 



Heredity in the Protozoa. — Studies on heredity in the Protozoa 

 have been distinctly hampered by the lack of conclusive infor- 

 mation on the entire life cycle in all but a relatively few species. 

 Some forms, as far as known, reproduce by simple division. 

 Here, obviously, any mechanism for inheritance would be simple 



