34 PROTOZOOLOGY 



Feulgen's niicleal reaction. The vesicular nucleus is most com- 

 monly present in various orders of the Sarcodina and Mastig- 

 ophora. 



The compact nucleus (Fig. 2, b), on the other hand, contains a 

 large amount of chromatin substance and a comparatively small 

 amount of nucleoplasm, and is thus massive. The macronucleus 

 of the Ciliophora is almost always of this kind. The variety of 

 forms of the compact nuclei is indeed remarkable. It may be 

 spherical, ovate, cylindrical, club-shaped, band-form, moniliform, 

 horseshoe-form, filamentous, or root-like. The nuclear membrane 

 is always distinct, and the chromatin substance is usually 

 spheroidal, varying in size among different species and often even 

 in the same nucleus. In the majority of species, the chromatin 

 granules are small and compact, though in some forms, such as 

 Nydotherus ovalis (Fig. 3), they may reach 20^ or more in diame- 

 ter, and while the smaller chromatin granules seem to be solid, 

 larger forms contain alveoli of different sizes in which smaller 

 chromatin granules are suspended (Kudo, 1936). 



There is no sharp demarcation between the vesicular and 

 compact nuclei, since there are numerous nuclei the structures of 

 which are intermediate between the two. Moreover what appears 

 to be a vesicular nucleus in hfe, may approach a compact nucleus 

 when fixed and stained as in the case of Euglenoidina. Several 

 experimental observations show that the number, size, and 

 structure of the endosomes in the vesicular nucleus, and the 

 amount and arrangement of the chromatin in the compact nu- 

 cleus, vary according to the physiological state of the protozoan 

 concerned. The macronucleus may be divided into two or more 

 parts with or without connections among them and in Dileptiis 

 anser into more than 200 small nuclei, each of which is "composed 

 of a plastin core and a chromatin cortex" (Calkins; 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 

 suspended 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 micro- 

 nuclear chromatin substance responds 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 



