46 General Morphology of the Protozoa 



functions inferred. In Ciliophora, with the apparent exception of the 

 Protociliatia,^ nuclei are differentiated into micronuclei and macronuclei 

 which differ in size, in structure, and in behavior during fission and 

 conjugation. 



Vesicular nuclei 



The vesicular nuclei of Mastigophora, Sarcodina, and Sporozoa 

 vary so much in structure that morphological classifications are neces- 

 sarily arbitrary. However, it is possible to recognize two general types — 

 those with an endosome and those without. In the endosome-type (Fig. 1. 

 20, A-D, F) the chromatin lies between the nuclear membrane and a more 

 or less central body, the endosome. The endosome apparently does not 

 contribute directly, at least in a morphological sense, to the formation of 

 chromosomes. A negative Feulgen reaction, indicating the absence of 

 desoxyribonucleic acid, has been reported for the endosome in Euglenida, 

 Phytomonadida and trypanosomes (104) and in Entamoeba coli, E. his- 

 tolytica, Endolimax nana, and lodamoeba hiltschlii (228). In encysted 

 Giardia Ia?nblia, however, the endosome is intensely Feulgen-positive 

 (144). The endosome of Entamoeba miiris also gives a positive reaction 

 (226). The nucleus in Entamoeba (Fig. 1. 20, F) contains a small endo- 

 some and relatively little chromatin; that of Endolimax and lodamoeba 

 (Fig. 1. 20, D), a large endosome and a small amount of chromatin. The 

 well defined peripheral granules, adherent to the nuclear membrane and 

 commonly considered chromatin granules, are Feulgen-negative in Enta- 

 moeba muris (226), E. coli, and E. histolytica (228). The discovery that the 

 chromosomes develop from a zone of minute Feulgen-positive "granvdes" 

 around the endosome of these amoebae emphasizes the need for critical 

 study of the smaller protozoan nuclei. The nucleus of Euglenida (Fig. 

 1. 20, A, B) contains abundant Feulgen-positive chromatin and a rather 

 large endosome which is sometimes fragmented. The endosome disap- 

 pears early in mitosis in the Endamoebidae and phytomonad flagellates, 

 but it persists and undergoes division in Euglenida and such dinoflagel- 

 lates as Oxyrrhis marina (73). 



Nuclei without endosomes (Fig. 1. 20, E, G, H) may contain several 

 nucleoli which often disappear in mitosis, although they persist in Zelleri- 

 ella (31). The chromatin is usually distributed throughout the nucleus 

 and its appearance may suggest some sort of a nuclear framework or 

 "network." Such nuclei are characteristic of many Heliozoida, Radiola- 

 rida, Hypermastigida, Dinoflagellida, opalinid ciliates, and Sporozoa. 



^Although Konsuloff (140) has maintained that the Feulgen-negative endoplasmic 

 spherules of Opalinidae are macronuclei, this interpretation has not been accepted. 

 Furthermore. Metcalf's "macrochromosomes," supposedly homologous with the macro- 

 nuclear chromatin of other ciliates, are merely Feulgen-negative nucleoli (31). 



