36 PROTOZOOLOGY 



found extranuclear chromatin granules in many protozoans. 

 Finding such granules in the cytosome of Actinosyhaerium eich- 

 horni, Arcella vulgaris, and others, Hertwig (1902) called them 

 chromidia, and maintained that under certain circumstances, 

 such as lack of food material, the nuclei disappear and the chro- 

 matin granules become scattered throughout the cytosome. In 

 the case of Arcella vulgaris, the two nuclei break down completely 

 to produce a chromidial-net which later reforms into smaller 

 secondary nuclei. It has, however, been found by Belaf that the 

 lack of food caused the encystment rather than chromidia- 

 formation in Actinosphaerium and, according to Reichenow, 

 Jollos observed that in Arcella the nuclei persisted, but were 

 thickly covered by chromidial-net which could be cleared away 

 by artificial digestion to reveal the two nuclei. In Difflugia, the 

 chromidial-net is vacuolated or alveolated in the fall and in each 

 alveolus appear glycogen granules which seem to serve as reserve 

 food material for the reproduction that takes place during that 

 season (Zuelzer), and the chromidia occurring in Actinosphaerium 

 appear to be of a combination of a carbohydrate and a protein 

 (Rumjantzew and Wermel). Apparently the widely distributed 

 volutin (p. 95), and many inclusions or cytozoic parasites, such 

 as Sphaerita, which occur occasionally in different Sarcodina, 

 have in some cases been called chromidia. By using Feulgen's 

 nucleal reaction, Reichenow (1928) obtained a .diffused violet- 

 stained zone in Chlamydomonas and held them to be dissolved 

 volutin. Calkins (1933) found the chromidia of Arcella vulgaris 

 negative to the nucleal reaction, but by omitting acid-hydrolysis 

 and treating with fuchsin-sulphurous acid for 8-14 hours, the 

 chromidia and the secondary nuclei were found to show a typical 

 positive reaction and believed that the chromidia are chromatin. 

 Thus at present the real nature of chromidia is still not clearly 

 known, although many protozoologists are inclined to think that 

 the substance is not chromatinic, but, in some way, is connected 

 with the metabolism of the protozoan. 



The cytosome 



The extranuclear part of the protozoan body is the cytosome. 

 It is composed of the cytoplasm, a colloidal system, which may 

 be homogenous, granulated, vacuolated, reticulated, or fibrillar 

 in optical texture, and is almost ahvays colorless. The chromato- 



