EFFECTS OF REORGANIZATION 343 



It is difficult to distinguish between fluctuating or cyclical 

 variations and germinal variations and the distinction cannot be 

 realized where the germinal history is unknown. The difficulty 

 is increased by the fact that comparatively few life histories of 

 Protozoa are known. Many variations that have been recorded 

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

 viduals of the species. These correspond to differentiations in 

 ontogeny of Metazoa and have been more fully discussed in Chapter 

 VII. 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. 



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

 the genotype 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 have to so affect the germinal make-up that 

 reversions would not occur. Thus individuals formed by reversions 

 from the double Uroleptus described in Chapter VII (p. 245) never 

 regenerated the double organism but lived as single individuals of 

 Uroleptus mobilis (Series 91 of table, p. 338). Here the organi- 

 zation was unchanged although the new double type of organism 

 lived for four hundred and five days and divided 367 times. 



Variations due to environmental changes should be retained as 

 long as such changes are maintained. Thus Zuelzer obtained a 

 very different type of organism by transferring Amoeba verrucosa 

 from fresh to salt water. The variation lasted as long as the organ- 

 isms were kept in salt water but reverted to the original form on 

 transference to fresh water again. Jennings (1921) cites a number 

 of cases of bacteria in which the organization appeared to be per- 

 manently changed by a temporary change of drastic character in 

 the medium. Similar results have been obtained with Protozoa 

 where adaptations or responses of the organism to solutions of 

 gradually increasing concentrations or to slowly increasing tem- 

 perature changes have apparently become permanent, or at least 

 endure for many generations by division. Among the first, and the 

 more extensive of such experiments, were those of Dallinger and 

 Drysdale (1873) in connection with the life histories of different 

 flagellates. Dallinger (1907) in particular, working with remark- 

 able patience and perseverance for seven years was able to accustom 

 three species of flagellates which are described as Tetramitus ros- 

 tratus, Monas dallingeri, and Dallingeria drysdali to temperatures 

 which are fatal to these organisms under normal conditions of 60° F. 

 At the beginning of the experiment all individuals were killed by 

 a sudden change to 78° F., but by accustoming them to slowly 

 increasing temperatures acting for long periods they became 

 adapted to this condition. Such adapted individuals were then 



