36 



PROTOZOOLOGY 



distinct, and the chromatin substance is usually of spheroidal form, 

 varying in size among different species and often even in the same 

 nucleus. In the majority of species, the chromatin granules are small 

 and compact, though in some forms, such as Nydotherus ovalis 

 (Fig. 3), they may reach 20^ or more in diameter in some individuals. 



Fig. 3. Parts of four macronuclei of Nydotherus ovalis, showing chromatin 

 spherules of different sizes, X650 (Kudo). 



and while the smaller chromatin granules seem to be solid, larger 

 forms contain alveoli of different sizes in which smaller chromatin 

 granules are suspended (Kudo, 1936). 



There is no sharp demarcation between the vesicular and compact 

 nuclei, since there are numerous nuclei the structures of which are 

 intermediate between the two. Moreover what appears to be a 

 vesicular nucleus in life, may approach a compact nucleus when 

 fixed and stained as in the case of Euglenoidina. Several experimental 

 observations show that the number, size, and structure of the endo- 



