CHAPTER XI 
HEREDITY IN THE PROTOZOA 
While certain characteristics or processes in the 
Protozoa have been shown to be transmitted along 
fission lines, 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 lines, 7.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 likewise is 
divided into equivalent halves. In regard to the 
cytoplasm, the halves are at first generally unlike; 
in the more highly specialized 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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