INHERITANCE 769 



the recent discovery of diverse mating types in these organisms. This 

 discovery renders it possible to make any desired crosses as readily in 

 these organisms as in fruit flies or in rats. 



In general terms, the relations of nucleus and cytoplasm to inheritance, 

 revealed in crosses in the ciliates, may be expressed as follows. The 

 primary source of diversities in inherited characters lies in the nucleus. 

 But the nucleus by knov^n material interchanges impresses its constitu- 

 tion on the cytoplasm. The cytoplasm retains the constitution so im- 

 pressed for a considerable time, during which it assimilates and repro- 

 duces true to its impressed character. It may do this after removal from 

 contact with the nucleus to which its present constitution is due, and 

 even for a time in the presence of another nucleus of different consti- 

 tution. During this period, cytoplasmic inheritance may occur in vegeta- 

 tive reproduction. The new cells produced show the characteristics due 

 to this cytoplasmic constitution impressed earlier by a nucleus that is no 

 longer present. But in time the new nucleus asserts itself, impressing its 

 own constitution on the cytoplasm. Such cycles are repeated as often as 

 the nucleus is changed by conjugation. 



Literature Cited 



An extensive bibliography of contributions on the genetics of Protozoa prior to 

 1929 will be found in the author's Genetics of the Protozoa (1929). The present list 

 includes only articles referred to in the foregoing chapter. 



Calkins, G. N. 1919. Uroleptus mohilh Engelm. II. Renewal of vitality 



through conjugation. J. exp. Zool., 29: 121-56. 

 Dallinger, W. H. 1887. The president's address. J. R. micr. Sec, 1: 185-99. 

 De Garis, C. F. 1935. Heritable effects of conjugation between free individuals 



and double monsters in diverse races of Paramecium. J. exp. Zool., 71: 



209-56. 

 Diller, W. F. 1936. Nuclear reorganization processes in Paramecium aurelia, 



with descriptions of autogamy and "hemixis." J. Morph., 59: 11-67. 

 Dobell, C. 1924. The chromosome cycle of the sporozoa considered in relation 



to the chromosome theory of heredity. Cellule, 35: 169-92. 

 Erdmann, R. 1927. Endomixis bei Paramecium bursaria. S. B. Ges. Naturf. Fr. 



Berl., 1925: 24-25. 

 Hammerling, J. 1929. Dauermodifikationen. Handbuch der Vererbungswissen- 



schaft (Baur u. Hartmann), Bd. 1, Liefrg. II: 1-69. 

 Jennings, H. S. 1916. Heredity, variation and the results of selection in the 



uniparental reproduction of Difflug/a corona. Genetics, 1: 407-534. 

 1929. Genetics of the Protozoa. Bibliogr. genet., 5: 105-330. 



