STUDIES UPON AMOEBA 
315 
What is the full life cycle of Amoeba? Doubtless some species 
have a more complex c^'cle than others. Some of the earth 
Amoebae, so far as we know, reproduce onh' by binary fission, 
copulation occurring between nearly full sized individuals and no 
gametospores being formed. The Entamoebae (coh, histolytica 
and tetragena) have the same type of life cycle as theearth Amoeba. 
Schultze showed that Amoebae proteus, when in the full grown 
stage, reproduces by binary fission (fig. 25 a). Scheel^^ described 
the formation of small endoamoebospores to the number of six 
hundred or so to a cyst (fig. 25, d-f). These amoebpospores were 
not seen to copulate, and there is no reason to believe that they 
do so. Calkins^^ has described in large sized Amoeba proteus 
the presence of numerous neuclei (?) which he thought probably 
would give rise to the nuclei of gametes. It seems, however, not 
impossible that what Calkins observed were parasites within the 
.Ajnoebae. I am inclined to believe that the gemmulating Amoe- 
bae described in this paper are \moebae proteus. 
Are there three or more sorts of reproduction in the life cycle 
of Amoeba proteus? I doubt if this question will ever be answered 
by isolating one or a few individual Amoebae proteus and making 
them go through their whole life cycle under observation. The 
whole life cycle probably requires a year or more for its completion, 
and ic is doubtful if Amoebae can be reared for so long a time, and 
the environmental conditions so changed at the proper times, as 
to afford the necessary- stimuli to instigate each of the several 
sorts of reproduction that may belong in the one life cycle. There 
is no conclusive proof that the Amoebae described in this paper 
are Amoebae proteus, but the small '^radiosa" forms (fig. 26) 
look like young Amoebae proteus, and Amoeba proteus of the 
typical larger sort was very abundant in the material before it 
became foul. The evidence seems to make it probable that the 
phenomena described belong in the life C3Tle of Amoeba proteus 
Beitrage zur Fortpflanzung der Amoben, Festschrift zum siebzigsten Geburtstag 
V. Kupffer^s. 
" Evidences of a sexual cycle in the life history of Amoeba proteus. in Archiv. 
f. ProtistenskuTide, bd. v, 1904; and The fertilization of Amoeba proteus, in Bio- 
logical Bulletin, vol. xiii, 1907. 
THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 9, NO. 2. 
