22 



HANDBOOK OF PROTOZOOLOGY 



nuclear space, they are in some cases scattered throughout the 

 cytoplasm either temporarily or permanently. These extranu- 

 clear chromatin granules are known as chromidia. In Testacea, 

 such as Arcella (Fig. 4) and Euglypha (Fig. 1), there are chro- 

 midia surrounding the nuclei. They have been found by some 

 investigators to give rise to secondary nuclei through reorganiza- 

 tion, the original nuclei degenerating in the meantime. Accord- 

 ing to Calkins, in Dileptiis anser (Fig. 4) there occur a large 

 number of small spheroidal chromidia, each of which is com- 

 posed of a plastin core and a chromatin cortex. 



Contractile vacuoles 

 Cytostome 



Food vacuoles 



Nucleus 



Chromidia 



Fig. 4 a. A stained Arcella vulgaris showing the two nuclei and chromidia. 

 X350. 

 b. A stained Dilepius anser with s:attered nuclei or chromidia. 

 X about 100 (After Calkins). 



In Mastigophora or in other groups in which flagellate stages 

 occur, the body possesses a structure which is directly or in- 

 directly connected with the basal portion of the flagellum (Fig. 

 5). This body has sometimes been called the kinetonucleus, but 

 there is no evidence to indicate that it is a nuclear structure, 

 although in some forms it is connected with the nucleus by a 

 filamentous structure known as the rhizoplast. The term ble- 

 pharoplast, or kinetoplast, is to be used to designate such a struc- 



