330 BIOLOGY OF THE PROTOZOA 



did the primordial germ cell, or endothelial cell, from which it 

 came. Reorganization of the protoplasm of that endothelial cell 

 has taken place in its metamorphosis to an egg cell and is brought 

 about by the often-described process of ovogenesis and matura- 

 tion. In this phenomenon of endothelial cell metamorphosis we find 

 the homologue in Metazoa of the reorganization processes of the 

 Protozoa. 



The nearest approach to the metazoon egg and spermatozoon 

 condition amongst animal Protozoa is found in the group Coccidio- 

 morpha amongst Sporozoa. Here, no less than in Metazoa, the 

 fertilized egg is the beginning of a new life cycle or, by metagamic 

 divisions, gives rise to sporozoites, each of which is the beginning 

 of an independent life cycle with its characteristic phases and 

 differentiations. Few biologists would question the application to 

 Sporozoa of the term life cycle, and yet no single individual sporo- 

 zoon has ever been followed through the sequence of changes from 

 fertilization to fertilization. This cyclical history of Sporozoa is 

 forgotten by those who speak of a life cycle in Protozoa as a myth. 

 They have in mind only the ciliated Infusoria and the phenomena of 

 conjugation; indeed the controversy over the effects of fertilization 

 in Protozoa has been limited almost exclusively to the Infusoria. 



Actual experiments to test the effects of conjugation on vitality 

 of the Infusoria have been few in number, the majority of investi- 

 gators stopping with experiments to determine the need of conjuga- 

 tion, i. e., whether or not vitality as measured by the division- 

 rate actually undergoes a diminution to a point where death ensues 

 if fertilization fails (see Chapter VII). Jennings (1921) has pointed 

 out that Maupas himself never claimed that the power to reproduce 

 is restored by conjugation, although his experiments did lead him to 

 the conclusion that ciliates undergo senile degeneration and natural 

 death. This inconsistency on Maupas' part requires some explana- 

 tion here for it is usually overlooked. His general conclusion is 

 carried in the statement: "In regard to Infusoria my culture 

 experiments have demonstrated that these Protozoa do not escape 

 the general law of senescence" (1888, p. 273). From this conclusion 

 we would naturally infer that senescence means a weakening of 

 the general physiological processes including the power to repro- 

 duce by division. But Maupas apparently had no such conception 

 of senescence for he adds: "The power of multiplication follows 

 no such diminishing and parallel course. It is maintained almost 

 intact even a long time after the other functions, and the entire 

 organism, are shown to be greatly reduced by senile degeneration" 

 (1888, p. 273). 



The inconsistencies in Maupas' conclusions have been pointed 

 out in another place (Calkins, 1923); it is sufficient here to state 

 that exact data in the form of daily records of divisions were kept 



