2 28 GARY N. CALKINS. 



Explanation of Plate XI. 



The photographs are from sections, stained with iron-hsematoxylin, of the same 

 specimens of Amoeba proteus that were pictured in my previous paper on " Evidences 

 of a Sexual-cycle in the Life-history of Amoeba proteus. The magnifications vary 

 from 550 diameters (Fig. 13) to 2,000 diameters (Figs. 9 and 10) . 2 



Fig. I. Part of section of Amoeba with about 30 primary nuclei some of which 

 have begun to fragment. The chromatin is massed in a characteristic manner about 

 the periphery while the small points in the center are the karyosomes of the future 

 secondary nuclei. At this stage there are few secondary nuclei in the cytoplasm. X 

 1,000. 



Fig. 2. Section from the amoeba represented in Fig. 7 of my previous paper. 

 The majority of the primary nuclei have fragmented and the cell body is spotted with 

 the secondary nuclei. These may be seen forming in the large primary nucleus (/)■ 

 The photograph also shows many stages in the fusion of the secondary nuclei. At 

 (a) two are seen with the peripheries in contact ; at (b) the bodies are beginning to 

 fuse ; at (c) and (d) fusion of bodies is completed, while the karyosomes have not 

 yet fused but lie facing one another (if this were division the karyosomes would be 

 elongated in the direction at right angles to this) ; at (e) there is an apparent double 

 fertilization ; at (,§-) the karyosome from the upper nucleus has migrated into the 

 lower nucleus before fusion of the nuclei is complete. X I )5°°- 



Fig. 3. Primary nucleus with brood of young secondary nuclei within it and 

 several secondary nuclei in various stages of fusion (a), (/;) and (r) representing 

 different stages in the process. X I >35°- 



Fig. 4. Primary nucleus with most of the secondary nuclei gone. Some 

 secondary nuclei below in different stages of early fusion, while above are two later 

 stages of union. X I )5°°- 



Fig. 5. Primary nucleus in the process of liberating secondary nuclei. Two 

 fully formed secondary nuclei are passing into the cytoplasm at (a), while others not 

 yet formed remain in the nucleus. Fig. 7 is a deeper section of the same primary 

 nucleus showing the fully formed secondary nuclei within it. X I )5°°- 



Fig. 6. Section of an amoeba in which all the primary nuclei (a), (b), (c) are 

 fragmenting and disintegrating while the secondary nuclei are in various stages of 

 fusion. The section was injured by the objective so that some of the pairs of 

 secondary nuclei are spread. X I ! 5 00 - 



Fig. 7. Section of same nucleus as that shown in Fig. 5, showing brood (a) of 

 secondary nuclei not yet liberated. X l >5°°- 



1 The actual dimensions in the photographs must be increased by one fifth to give 

 the magnifications stated. 



