224 GARY N. CALKINS. 



morphological grounds alone, cannot be entirely refuted, I firmly 

 believe that they are not parasites but developmental phases of 

 Amceba proteus. My reasons for this belief may be briefly sum- 

 marized as follows : First, the early stages of nuclear increase 

 are present in specimens of Amoeba in which there are none of the 

 supposed parasites. Second, the supposed parasites must originate 

 inside of the supposed degenerating nuclei, for, as Figs. 2, 5, 6, 

 7 and 8 clearly show, the structures under consideration first arise 

 inside of the nuclei, and wander outside by dissolution of the nu- 

 clear membrane. Third, if they are parasites they must con- 

 jugate inside of the endoplasm of the Amceba, for, as we have 

 seen above, there are no good grounds for interpreting these 

 structures as dividing forms. Fourth if the structures in question 

 are conjugating parasites the conjugation leads to further develop- 

 ment within the protoplasm of the host cell without any protect- 

 ing membranes against the resistance of the host cell. Fifth, if 

 these things are parasites, then the secondary nuclei of Arcella, 

 Polystomella and Entamoeba must likewise be parasites, for the re- 

 semblance between the several cases is too strong to allow 

 another interpretation. Finally, if they are parasites, they must 

 wander into the nuclei of Amceba proteus in the form of germs 

 too small to be recognized and grow there into larger nucleus- 

 like bodies which emerge from the nucleus and conjugate, and 

 all this without disturbing the physiological equilibrium of the 

 Amoeba, and without effecting any pathological change such as 

 formation of vacuoles or spaces about themselves (cf. Figs. 2, 

 3, 4). The evidence, therefore, is altogether in favor of the 

 nuclear character of these questionable structures, and their union, 

 I believe, can be interpreted in no other way than as the fertiliza- 

 tion of this universal rhizopod. 



The fertilization of Amceba proteus has been sought for by biol- 

 ogists for decades. Many observations have been published on 

 phenomena supposed to be conjugation processes, but these in 

 the main, have turned out to be cases of plastogamy, common 

 amongst the rhizopods, or cases of engulfing of one by another. 

 If the fertilization were any ordinary process similar to what 

 occurs in other allied forms, there seems little likelihood that it 

 would have been overlooked for these many years. But occurring 



