THE FERTILIZATION OF AMCEBA PROTEUS. 



GARY N. CALKINS. 



Three years ago I published a short paper entitled " Evi- 

 dences of a Sexual Cycle in the Life-history of Amceba proteus " 1 

 in which I described the formation of chromidium in one 

 life-phase of this common rhizopod and the subsequent 

 formation of secondary nuclei. The latter were interpreted 

 as nuclei of the supposed gametes which were collected in 

 a cyst. The supposed gametes were in no case seen to 

 emerge from the cyst and conjugation was not observed. 

 Many of the structures observed in the amoebae at this time, 

 could not be interpreted in terms of the corresponding phases of 

 other fresh water rhizopods, a curious division of the granules 

 (represented in Plate 3, Fig. 23 of the former paper), and an 

 equally enigmatical series of spheres with peripheral granules 

 (represented in Figs. 12, 24 and 27), being particularly hard to 

 homologize with other known phases in rhizopod development. 

 Had I not been busy with other work at the time, I might have 

 discovered that the very material used for these " evidences " 

 would furnish proof of the actual fertilization, for this last spring, 

 hoping to find some trace of a maturation process in rhizopods at 

 the period of chromidium formation, I dissolved off the cover 

 glasses from the amoebae which were preserved in balsam, em- 

 bedded them in paraffine, cut them one by one in sections 

 from three to five microns in thickness and discovered the 

 method of fertilization. A careful examination of the so-called 

 " dividing granules " in these sections revealed the fact that what I 

 had interpreted in the total mounts as dividing forms of the 

 chromidial granules, were actually minute nuclei in the process of 

 fusion, and that,. instead of division, it was the process of fertiliza- 

 tion, while the encysted bodies with the peripheral granules were 

 stages in the development of these fertilized nuclei. The ma- 

 terial, unfortunately, is still not complete enough to give the 

 details of the chromatin changes as thoroughly as I wish, but 

 there are enough stages to enable us to clear up this sexual phase 



1 drck. f. Protistenk., V., 1904, pp. I-16. 



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