PROTOZOA 



21 



possibly to be interpreted as the multiplication of units in a poly- 

 energid nucleus by cryptomitoses. 



In the Ciliophora (other than the Opalinidae and the Chonotricha) 

 the nucleoplasm, which in other protozoa is contained in one nucleus 

 or in several which are all alike, is divided into two portions, a large 

 amitotic meganucleus which breaks up periodically in "endomixis" 

 (see p. 30) and also at conjugation, and one or more small micronuclei, 

 by division of one of which the pronuclei of conjugation are provided 

 and the meganucleus replaced when the latter disintegrates. Indi- 



Fig. 20. Stages in the mitosis (cryptomitosis) of Haplosporidium limnodrili. 

 After Granata, A, Resting nucleus : the spindle here persists. B, Metaphase. 

 C, Anaphase. D, Telophase, chr. chromatin; kar. karyosome; spd. spindle. 



viduals without micronuclei have been observed and kept through 

 several asexual generations. Thus the meganucleus is capable of 

 conducting by itself the normal vegetative existence of the individual, 

 though the absence of this nucleus at syngamy shows that it does not 

 establish the characters of the race. That function must be performed 

 by the micronucleus, but, since the latter does not exist without the 

 meganucleus, save for a brief period during conjugation, it presumably 

 does not regulate the life of the individual. The chromatin of the 



