246 EILEIES [Vor. XII. 
The volume of the smallest Stentor found was thus equal to 
a sphere of somewhat less than 80m in diameter. Not one of 
the hundreds of smaller nucleated parts regenerated, though I 
found one part, 7Im in diameter in spherical form, which had 
assumed a fairly typical form of semi-contraction and possessed 
a single bead of the nucleus; anterior and posterior ends (or 
foot) were thus recognizable, but there was neither oesophagus 
nor adoral membranellae present. Even if we admit this as 
regenerated, which I do not, it does not essentially alter the 
final result. 
My conclusion is, therefore, that nucleated parts of Stentor 
polymorphus of less volume than a sphere of 80 (approxi- 
mately) in diameter are incapable of regeneration; nucleated 
parts of greater volume are capable under favorable conditions 
of complete regeneration. 
The main results hitherto reached on the merotomy of the 
Protozoa can be summarized as follows : 
1. Cytoplasm without nucleus is incapable of regeneration 
(Nussbaum, Gruber, Verworn, Balbiani, and others). This I 
can confirm. (Verworn has shown that the isolated central 
capsule of Zhalassicola nucleata from which the nucleus has 
been removed is capable of partial regeneration, but it soon 
goes to pieces. Gruber has shown that if a Stentor in process 
of fission be transversely divided so that the posterior part 
receives no nucleus, this part is nevertheless able to regen- 
erate.) 
2. Nucleus without cytoplasm is incapable of regeneration. 
(Verworn, Balbiani.) This also I can confirm. 
3. Portions of the body consisting of nucleus and cytoplasm 
are capable of regeneration. To this [ must add: provided that 
the amount of cytoplasm exceed a certain minimal volume 
(which in the case of Stentor at any rate is quite considerable). 
This amounts to a demonstration of Verworn's view that 
vegeneration tn the Protozoa ts due to the reciprocal interaction 
of nucleus and cytoplasm. Organization resides in the cytoplasm 
as wellas in the nucleus. How otherwise are we to explain the 
fact that a difference in the amount of cytoplasm alone (equiv- 
alent to the difference in volume of two spheres of SO and 70 
—_ 
