CHAPTER V. 



REPRODUCTION. 



GENERAL REPRODUCTION; ALL REPRODUCTION 

 CELL DIVISION. 



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, subject to minor varia- 

 tions of a fluctuating character in the course of a normal life history, 

 or subjected experimentally to all kinds of unusual environmental 

 conditions, remains fundamentally unchanged. T}T)es modified 

 through amphimixis or through permanent modifications of the 

 environment may lead to divergent types. This conservatism or 

 fixity of tx-pe 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 organ- 

 ization 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 amongst 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 dift'erentiations which may or may not be visibly indi- 

 cated by structural changes (see Chapter X). PHtimately its possi- 

 bilities of further vitality as a single individual are exhausted and 

 it undergoes its final manifestation of vitalit\'. The significance 

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

 whereby the organization is further parcelled 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 parcelled 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, 



