CHAPTER II 



GENERAL ACCOUNT OF THE GERM-CELL CYCLE 

 IN ANIMALS 



It will be impossible to present in this chapter even 

 a general account of all the variations in the germ- 

 cell cycle that are known to occur in animals. It 

 will be necessary, therefore, to restrict ourselves to 

 the series of events that occurs in the majority of 

 animals, mentioning as many of the more notable 

 variations and exceptions as possible without causing 

 confusion. It also seems advisable to consider 

 the germ-cell cycles in the Protozoa and the Meta- 

 zoA separately. 



Protozoa. Weismann, in his classical essays 

 on the germ-plasm, argues in favor of the view that 

 the Protozoa are potential germ cells, and, since new 

 individuals arise by division of the parent cell into 

 two or more parts, that natural death does not occur. 

 The Protozoa are consequently also potentially 

 immortal. The Metazoa, on the other hand, 

 possess a large amount of somatic substance which 

 always dies a natural death. It has often been 

 pointed out that a Protozoon, although consisting 

 of but a single cell, performs most of the physiological 

 activities characteristic of the larger, complex 

 Metazoa, and that certain parts of the Protozoon 



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