174 University of Calif orniaPuilications in Zoology [Vol. 20 



The endoplasm, on the other hand, is coarsely vacuolated in the 

 free stage and may be loaded with food vacuoles containing bacteria, 

 red blood corpuscles, and occasionally a cyst of CMlcnnastix (pi. 19, 

 fig. 6), or other particles from the faeces. This marked vacuolation 

 and the great abundance of food contents of all sorts distinguish it 

 at once from Endamoeba dysenteriae, but lead to confusion with 

 Endamoeia coli in the absence of pseudopodia. 



The food vacuoles and the fluid-filled ones which are scattered 

 among them may crowd to the periphery of the body locally, or they 

 may leave a narrow peripheral zone relatively free from such inclu- 

 sions. They are moved about freely in the mobile endoplasm, as is 

 the nucleus. The latter often lies on the very edge of the endoplasm. 



The nucleus in the free stage presents different aspects, according 

 to the degree of destaining and to phases of the mitotic cycle. The 

 chromatin is distributed in the peripheral zone on the nuclear mem- 

 brane and in a karyosome separated from the former by an inter- 

 mediate clear zone. The peripheral chromatin is broken up into a 

 relatively thin sheet (as compared with that of Endamoeba coli) of 

 somewhat uniform particles flattened against the membrane and giving 

 to it in some instances a crenate inner margin in optical section. 

 Occasionally a larger particle is interpolated. This layer is not so 

 thick as in Endamoeba coli, but is much thicker in the free amoebae 

 than in the nuclei of the older cysts in Councilmania, and is also thin- 

 ner in free amoebae when the karyosome is enlarged and mitosis is 

 approaching. 



The karyosome in the resting nucleus is generally somewhat ex- 

 centric, as it is in E. coli. Not rareh^ it is quite excentric. It may 

 be spheroidal or angular and has a very narrow, not always concentric, 

 clear halo about it. This halo can not be found in many nuclei, espec- 

 ially those in which mitosis is approaching. In such nuclei the karyo- 

 some takes on the form seen in the cysts and has a much larger volume 

 of chromatin, which breaks up into particles forming a sphere, ring, 

 or reniform mass as the spireme stage approaches (pi. 19, figs. 7, 8). 



The intermediate zone is free from distinct structural modifications. 

 There may be a faint reticulum and occasionally a few minute chrom- 

 atin granules in it in heavily destained preparations. "We are un- 

 able, with our method of fixation and available eosins, to demonstrate 

 in it ajiy eosinophile granules such as Dobell (1920, pi. 2, figs. 32-34) 

 finds in the amoeba which he regards as the free stage of his lodamoeba 

 iuetschUi. Otherwise there is enough in common between free Conn- 



