220 GARY N. CALKINS. 



in the cycle of Amoeba proteus and to bring together the observa- 

 tion of Scheel and earlier observers and to combine them in one 

 completed life history. 



As described in my earlier paper, this phase of the life-history 

 of Amoeba proteus is characterized by the repeated division of the 

 nucleus until many nuclei are present in the cell, 72 to 80 being 

 the largest numbers observed in any one organism. These nu- 

 clei then fragment, and the chromatin granules, liberated by rup- 

 ture of the nuclear membranes, are distributed in the cytoplasm. 

 This fragmentation continues until all but one of these primary 

 nuclei are thus broken up, this one remaining as a residual nu- 

 cleus, while the cytoplasm becomes packed with the chromatin 

 fragments which I had interpreted as the chromidium. Stages in 

 this disintegration of the nuclei are shown in Figs. 6, 7, 8, 19-26,. 

 of my earlier paper. These granules were described as increas- 

 ing in size, dividing and ultimately forming the hollow spheres 

 with peripheral granules in the encysted stage (Figs. 23, 24 and 

 27* of the former paper). 



Now that the amoebae have been removed from the slides, sec- 

 tioned, and stained in iron-haematoxylin, the structure of the 

 granules is brought out with more vivid clearness than in the 

 total preparations stained with picro-carmine. The disintegration 

 of the primary nucleus can be followed step by step in the sec- 

 tions and the origin of the gametic nuclei, as I may now call 

 them, can be easily traced. 



The first indication of fragmentation is the collection of the 

 chromatin about the inner walls of the primary nucleus. Com- 

 paratively large reservoirs are massed about the periphery in this 

 way (Fig. 1), but in the meantime chromatin granules in the interior 

 of the nuclei are assuming a definite form, while a less deeply 

 staining, more homogeneous cortical zone of nuclear plasm col- 

 lects around them. The peripheral granules are also used to 

 form similar minute nuclei which, apparently as soon as formed, 

 move out into the cytoplasm. Here they are clearly marked 

 nuclei, consisting of a densely staining central granule or karyo- 

 some with a more faintly staining cortical zone (Figs. 2, 3, 4, 5, 

 6, 7). The bulk of the primary nuclei is metamorphosed into these 

 secondary nuclei, which are so small and so numerous that they 

 give a characteristic granular appearance to the cell. 



