16 PARASITIC AMOEBA OF MAN. 



tains a minute centriole or centrosome, and in one or 

 two species is of service in differentiation. Within 

 the nucleus there occurs a varying amount of 

 chromatin, the arrangement of which is of value in 

 distinguishing species. In some species the chromatin 

 is collected in masses upon the nuclear membrane, 

 while in others it is distributed throughout the 

 nucleus in the form of a network enclosing a well 

 defined karyosome. The amount of chromatin varies 

 in different species, in some being almost absent, 

 while in others it constitutes the greater portion of the 

 nucleus. A certain amount of achromatic substance 

 which is unstainable is contained within the nucleus. 

 In living specimens the chromatin appears as brightly 

 refractile granules or masses situated within the 

 nucleus or arranged around the nuclear membrane, 

 while in stained specimens it takes the ruby red color 

 characteristic of this substance if any modification of 

 the Romanowsky stain is used. 



Besides the nuclear chromatin certain species of 

 amoeba?, when stained, present a large amount of 

 this substance lying within the endoplasm. In such 

 instances the chromatin is distributed throughout the 

 endoplasm in the form of granules or threads or as 

 irregular masses which may be situated near the 

 periphery of the organism. The chromatin situated 

 within the endoplasm is known as chromidia or idio- 



