CHAPTER VI. 

 REPRODUCTION. 



Of all the marvels associated with the Protozoa there is nothing 

 more staggering to the imagination than the fixity of type which 

 their protoplasm manifests. The genotype, represented by the 

 derived organization, subject to minor variations of a fluctuating 

 character in the course of a normal life history, or subjected experi- 

 mentally to all kinds of unusual environmental conditions, remains 

 fundamentally unchanged. Types modified through amphimixis or 

 through permanent modifications of the environment may lead to 

 divergent types. This conservatism or fixity of type is a function 

 of the organization which has been continuous in the past and will 

 be continuous in the future. The activities which take place in 

 the organization, the sum total of which constitute vitality, are 

 discontinuous, they have been and will continue to be dependent 

 upon the interactions between organization and environment. 



The single individual which we study under the microscope has 

 had no such history in the past and no promise for the future; its 

 span of life as an individual is measured by hours or days only. It 

 is the temporary trustee of a small portion of an organization which 

 has been parceled out among unknown myriads of similar trustees. 

 Its metabolic activities are the interactions within the organization 

 and as a result of these activities the fluctuating variations charac- 

 teristic of the genotype follow one after another in the form of 

 inevitable differentiations which may or may not be visibly indi- 

 cated by structural changes (see Chapter VII). Ultimately its possi- 

 bilities of further vitality as a single individual are exhausted and 

 it undergoes its final manifestation of vitality. The significance 

 of this final act is a function of all genotypes and of all organizations 

 whereby the organization is further parceled out to two or more 

 trustees. It is reproduction by division, which by reason of its 

 universal occurrence is one of the most characteristic properties of 

 protoplasm. 



There is no doubt that division of the cell is a phenomenon of 

 deep-reaching significance; we shall endeavor to show that the 

 organization as parceled out to the descendants by division is not 

 a mere equal division of the protoplasm of the individual with its 

 load of metaplastids and other modifications of the organization, 

 but a renewed or purified organization such as the individual received 

 when it was formed. Unlike Metazoa, with the processes of division, 

 the old derived organizations of Protozoa are lost by absorption, 



