HEREDITY AND VARIATIONS IN PROTOZOA 583 



A single individual of Chilodon iincinatus was isolated by 

 MacDoiigall (1925) in December. Its progeny were maintained 

 in pure line cultures until lost in June. In May, larger forms ap- 

 peared in the cidtures and these increased until they out-numbered 

 the smaller forms few of which could then be found. Cytological 

 examination showed that the larger form was morphologically 

 identical with the smaller form, with the exception of the micro- 

 nuclei in which the chromosomes were eight in number as against 

 fom* in the smaller form. MacDcjiigall worked out the meiotic divi- 

 sions for both types and found a similar history in both (Fig. 238) 

 and correctly interprets the tetraploid form as a mutant from the 

 ordinary diploid type. 



The Protozoa, finally, cannot be regarded as simple organisms 

 which may be changed in structure or function at will. Each t}npe 

 has a remarkable tenacity of life which we believe is the same as 

 organization and which may be temporarily modified by environ- 

 mental changes but in which permanent changes are rare and 

 when they occur must come apparently from within. Life or 

 organization on the one hand, is continuous and has been handed 

 down from the indefinite past to the species which we know today 

 through their ancestors. Vitality on the other hand is discontinuous 

 and variable and is manifested by the sum of activities which take 

 place in the organization at any time. Death is not of necessity 

 the cessation of vitality but the disintegration of the organization 

 after which vitality is impossible. 



SPECIAL BIBLIOGRAPHY. 



Calkins, G. N., and Gregory, L. H. : 1913, Variations in the Progeny of a Single 

 Ex-conjugant of Paramecium caudatum. Jour. Exper. Zool., vol. 15. 



DoBELL, C. C: 1915, Some Recent Work on Mutation in Microorganisms, Jour. 

 Genet., vol. 2. 



Erdmann, R., and Woodruff, L. L.: 1916, The Periodic Reorganization Process 

 in Paramecium caudatum, Jour. Exper. Zool., vol. 20. 



Jennings, H. S.: 1916, Hereditj-, Variation, and the Results of Selection in the 

 Uniparental Reproduction of Difflugia corona, Genetics, vol. 1. 



Jennings, H. S., and Lashley, K. S.: 1913, Biparental Inheritance and the Ques- 

 tion of Sexuality in Paramecium, Jour. Exper. Zool., vol. 14. 



JoLLOS, V. : 1916, Die Fortpflanzung der Infusorien und die potentielle Unsterblich- 

 keit der Einzclligen, Biol. Cent., vol. .36. 1921, Experimcntelle Protistenstudien, 

 Arch. Prot., vol. 43. 



MacDougall, M. S.: 1925, Cytological Observations on Gymnostomatous Ciliata 

 with a Description of the Maturation Phenomena in Diploid and Tetraploid 

 Forms of Chilodon uncinatus, Quart. Jour. Mic. Sci., vol. 69 (new series). 



Pascher, a.: 1916, Ueber die Kreuzung einzelliger haploider Organismen: Chlamy- 

 domonas, Ber. Deutsch. Bot. Ges., 1916, vol. 34. 1918, Ueber die Beziehung 

 der Reduktionsteilung zur Mendelschen Spaltung, Ibid., 1918, vol. 36. 



Woodruff, L. L., and Erdmann, E.: 1914, A Normal Periodic Reorganization 

 Process Without Cell Fusion in Paramecium, Jour. Exper. Zool., vol. 17, No. 4. 



