44 PROTOZOOLOGY 



divided into two or more parts with or without connections among 

 them and in Dileptus anser into more than 200 small nuclei, each of 

 which is "composed of a plastin core and a chromatin cortex" (Cal- 

 kins; Hayes). 



In a compact nucleus, the chromatin granules or spherules fill, as 

 a rule, the intranuclear space compactly, in which one or more endo- 

 somes (Fig. 2, i) may occur. In many nuclei these chromatin granules 

 appear to be suspended freely, while in others a reticulum appears to 

 make the background. The chromatin of compact nuclei gives a 

 strong positive Feulgen's nucleal reaction. The macronuclear and 

 micronuclear chromatin substances respond differently to Feulgen's 

 nucleal reaction or to the so-called nuclear stains, as judged by the 

 difference in the intensity or tone of color. In Paramecium caudatum., 

 P. aurelia, Chilodonella, Nyctotherus ovalis, etc., the macronuclear 

 chromatin is colored more deeply than the micronuclear chromatin, 

 while in Colpoda, Urostyla, Euplotes, Stylonychia, and others, the 

 reverse seems to be the case, which may support the validity of the 

 assumption by Heidenhain that the two types of the nuclei of 

 Euciliata and Suctoria are made up of different chromatin sub- 

 stances — idiochromatin in the micronucleus and trophochromatin 

 in the macronucleus — and in other classes of Protozoa, the two kinds 

 of chromatin are present together in a single nucleus. The macro- 

 nucleus and the micronucleus of vegetative Paramecium caudatum 

 were found by Moses (1950) to possess a similar nucleic acid-protein 

 composition; namely, similar concentrations of total protein, non- 

 histone protein, desoxyribose nucleic acid and ribose nucleic acid. 

 Of the two latter nucleic acids, ribose nucleic acid is said to be pres- 

 ent in a larger amount than desoxyribose nucleic acid in both nuclei. 

 It may be considered that the two nucleic acids occur in different 

 proportions in the two nuclei. 



Chromidia. Since the detection of chromatin had solely depended 

 on its affinity to certain nuclear stains, several investigators found 

 extranuclear chromatin granules in many protozoans. Finding such 

 granules in the cytoplasm of Actinosphaerium eichhorni, Arcella vul- 

 garis, and others, Hertwig (1902) called them chromidia, and main- 

 tained that under certain circumstances, such as lack of food ma- 

 terial, the nuclei disappear and the chromatin granules become scat- 

 tered throughout the cytoplasm. 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 



