MORPHOLOGY 37 



some in the vesicular nucleus, and the amount and arrangement of 

 the chromatin in the compact nucleus, vary according to the physio- 

 logical state of the whole organism. The macronucleus may be 

 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 general, the chromatin granules or spherules fill the intra- 

 nuclear space compactly, in which one or more endosomes may 

 occur. In many nuclei these chromatin granules appear to be sus- 

 pended freely, while in others a reticulum appears to make the 

 background. The chromatin of compact nuclei gives a strong posi- 

 tive Feulgen's nucleal reaction. The macronuclear and micronuclear 

 chromatin substances respond differently to Feulgen's nucleal re- 

 action 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. 



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 cytosome of Actinosphaeriu7n 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 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 Belar 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 



