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 Mrta- 
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 Merazoa, 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 Prorozoon, 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 Protozo6n 
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