PROTOZOA 



23 



aggregation, as, for instance, in Actinosphaertum, but more often is 

 permanent except, sometimes, at division. Such a permanent en- 

 dosome is usually a nucleolus or an amphinucleolus, but is said 

 sometimes to consist solely of chromatin or of achromatic matter. 

 A permanent endosome consisting of plastin or chromatin, or both, is 



.nul 



kar.^ 



^'kan 



nu. 



Fig. 18. Nuclei of Protozoa. A, Polystomella crispa. B, Amoeba proteus. 

 C, Actinosphaerimn eichhorni. D, Naegleria bistadialis. E, Polytoma tivella. 

 F, Ceratiiim fusus. G, Stentor coeriileus. All highly magnified, to various 

 degrees. After various authors, cen.'i possible centriole; kar. karyosome, 

 containing a centriole in D; nu.' nucleoli or amphinucleoli. 



known as a karyosome. Two principal types of protozoan nuclei — the 

 dense and the vesicular — may be distinguished; there are, however, 

 intermediates between them, and they do not characterize each a 

 distinct branch of the phylum, but the dense appears to have arisen 

 more than once from the vesicular. In nuclei of the dense type the 

 achromatic part has a relatively firm consistency, and often exhibits, 



