488 BIOLOGY OF THE PROTOZOA 



posterior end as indicated in Fi^. 203, does not regenerate the lost 

 part (Calkins 1911, Peebles 1912). A membrane is formed over the 

 cut surface and cortical differentiations in the form of coordinat- 

 ing fibrils, basal bodies, cilia and trichocysts are produced. The 

 result is a characteristic truncated cell. When this divides division 

 occurs in the geometrical center of the organism as it was before 

 cutting and not in the center of the truncated cell (Fig. 203). Two 

 diverse cells result from division; one is normal and full-sized, the 

 f)ther small and truncated. It ver\' often happens that cutting in 

 this maimer induces deep-seated changes in the organization and 

 such that the precision of division phenomena in the truncated cell 

 is destroyed and incompletely divided cells or monsters result. 

 (Such monsters, one with 16 mouths, are illustrated in Fig. 203). 



Still further evidence of inter-divisional differentiation is shown 

 by the antecedent nuclear changes preparatory to division whereby, 

 in ciliates, macronuclear elements discard part of their substance into 

 the cytoplasm and fuse to form a single, usually ellipsoidal, macro- 

 nucleus which then divides (UronycJiia, Sfentor, Uroleptvs, Spi- 

 rosfomvm, etc.). Or in flagellates the entire kinetic complex is 

 absorbed in Lophomonos and several other types of flagellates (see 

 Chapter V). 



It thus appears that well-marked changes of the nature of differ- 

 entiations in the organization are taking place during the inter- 

 divisional metabolic period, and that transformations of the nature 

 of de-differentiations whereby the protoplasm is restored to the 

 labile condition of a young organism, occur with each division of 

 the cell. It is quite possible that this divisional reorganization is 

 adequate for the preservation of the protoplasm through long periods 

 of activity and may be the explanation of the long-continued life in 

 certain cultures of ciliates, or continued life of animal flagellates 

 in which fertilization processes are unknown. 



Other difterentiations occur in Protozoa which cannot be regarded 

 as inter-divisional in character. These are rather of a cumulative 

 nature and are not lost with the de-differentiation which occurs at 

 division. 



2. Cyclical Differentiations.— This second group of differentia- 

 tions are not manifested in every cell of a species but appear at 

 certain phases in the life history of the protoplasm composing any 

 series of individuals. They are racial therefore and correspond 

 roughly with periods in metazoon develo})ment such as youth, ado- 

 lescence and age. Some of these difterentiations are characteristic 

 of very young forms, occurring immediately after fertilization and 

 at no other time in the life cycle. Others make their appearance 

 later in the cycle and often after many generations by division. 

 These lead to and accompany the phenomena of fertilization and 

 include gamete formation and maturation stages. Still others 



