CHAPTER XI 

 HEREDITY IN THE PROTOZOA 



Wliile certain characteristics or processes in the 

 Protozoa have been shown to be transmitted along 

 fission hnes, and in this sense to be "inherited," 

 nevertheless it is a fact that almost nothing has 

 been found to show that single characters are 

 segregated in a Mendelian sense, although there are 

 indications that segregation of some sort takes 

 place after conjugation. It may therefore appear 

 questionable to use the word heredity, except in a 

 very general way, in describing what occurs in the 

 Protozoa. 



Nearly all of the cases studied in protozoa relate 

 to fission hnes, i.e., to individuals that have been 

 produced by continued division of parent indi- 

 viduals, each giving rise to two daughter individuals. 

 In such asexual reproduction it has been commonly 

 assumed, on the basis of observation, that both 

 micronucleus and macronucleus are divided into 

 identical parts, and that the cytoplasm hkewise is 

 divided into equivalent halves. In regard to the 

 cytoplasm, the halves are at first generally unlike; 

 in the more highly speciahzed forms of infusorians 

 the ends of the body are differently organized, and 

 these differences may persist through the division, 

 but are at once set straight by regeneration of the 



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