566 BIOLOGY OF THE PROTOZOA 



such stages in the hfe history. The described cases of autogamy 

 during encystment of Enflamceba coll and EndamoEha iniiris (see 

 Chapter XI), although the facts are doubted by many, is evidence 

 in this direction. So also are the peculiar fertilization phenomena 

 in Amoeba dipJoidea (Fig. 230), or the presence of mitotic figures 

 in encysted Rhizopoda, for example Kartjamcpba falcata (Kofoid 

 and Swezy, 1924; Fig. 233). 



The general and philosophical aspects of the phenomena described 

 above, particularly those pertaining to the so-called physical 

 immortality of the ciliates, are important or not according to the 

 individual point of view. To my mind the phenomena in these 

 forms lead to the conclusion that Protozoa and INIetazoa are funda- 

 mentally alike in respect to protoplasmic continuity and proto- 

 plasmic death, the difference between them is })oinid up with our 

 definitions of the "individual." So far as immortality of Protozoa 

 is concerned, Hertwig's (1914) conclusions appear to sum up the 

 situation: "However these investigations may turn out, one may 

 say this now, that the doctrine of the immortality of the Protozoa 

 in the form estal)lished by Weismann at a time when we did not 

 know anything of the fertilization processes of the Protozoa, 

 cannot be retained. The beautiful investigations of Erdmann and 

 Woodruff do not detract from my conception based on former 

 work and repeated here, but furnish a new affirmaticm that death in 

 imany-celled animals is the result of peculiarities which are present 

 in everything that is alive, and that the life process contains within 

 itself the germ of death and that the harm connected with it (death) 

 may be postponed in Protozoa by reorganization processes. In 

 many-celled animals however, these cannot be applied, the more 

 the life of the single cell depends on the total organization." 

 (Hertwig, 1914, p. 580.) 



II. HEREDITY AND VARIATIONS IN PROTOZOA. 



Owing to the relative simplicity of the organisms with which we 

 are dealing there are few structural characteristics that can be used 

 in a study of variations. Variations in size are often noted but 

 these in themselves do not furnish reliable data, a D'deptus anser for 

 example may be 250 microns in length or only 25 microns (P'ig. 6, 

 p. 28) according to the food it gets. Similar differences due to 

 temporary conditions are evident in all organisms that are studied 

 for a sufficient length of time. In a mixed population, however, 

 size differences may indicate fixed variations as was clearly shown 

 by Jeimings (1909) for Paramecium (Fig. 234). 



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 



