THE FERTILIZATION OF AMCEBA PROTEUS. 221 



The earliest stages of secondary nucleus formation within the 

 nucleus are so minute that they would scarcely be taken for the 

 same things as the cytoplasmic nuclei. Stages in growth, how- 

 ever, can be found in which the size varies from these extremely 

 minute ones to the full size nuclei of the cytoplasm (Figs. I, 2). 

 Fig. 5 shows a primary nucleus in the process of fragmentation 

 with two full size secondary nuclei emerging at a while within 

 the nucleus one or more large ones can be made out. Figs. 6 

 and 7 and Fig. 8 show similar late stages in secondary nucleus 

 formation. 



After emerging from the primary nucleus the secondary or 

 gametic nuclei fuse and the stages in the process can be followed 

 step by step in the fixed material. In such fixed material, how- 

 ever, the argument may be raised that it is equally possible to 

 trace the history of stages in the opposite direction and claim that 

 the process is one of division and not conjugation, this being one 

 of the serious difficulties in working on preserved organisms. 

 Nevertheless the evidence is so strong that there exists no doubt 

 whatsoever in my own mind that we are dealing with conjugation 

 and not with division. In the first place the number of gametic 

 nuclei is far greater than the number of sporoblasts which make 

 up the later cyst stage. In one specimen I counted more than 

 three hundred gametic nuclei in addition to eighteen as yetunfrag- 

 mented primary nuclei, while the number of sporoblasts in the later 

 stages does not exceed 250 in any one of the specimens in my 

 possession. Numerical relations indicate, therefore, that union 

 rather than division takes place. In the second place the indi- 

 viduals of the pairs of nuclei that are fusing, are of the same 

 size as the single ones. If they were dividing the daughter 

 nuclei would be considerably smaller. Size here, however, is so 

 variable that I do not lay much stress on this argument. In the 

 third place, if the nuclei were dividing we should find dumb-bell 

 shaped figures with the diameter of the nuclei drawn out at right 

 angles to the plane of division. This is not the case, the minute 

 nuclei remaining as spherical as though not in contact. In the 

 fourth place we should expect to find connecting strands of chro- 

 matin substance between the recently divided karyosomes if it 

 were a case of division, but no such, connecting strands exist. In 



