No: t.)] THE, SMAELEST' PARTS OF STENTOR. 247 
micromtillimeters respectively) determines the occurrence of regen- 
eration ? 
As regards the bearing of the results on the limits of divisi- 
bility of living matter: we are not concerned here with the 
question of the ultimate constitution of protoplasm, its com- 
position of any ultimate vital elements whatsoever, but merely 
with the question propounded by Loeb, ‘‘ What is the order of 
magnitude of the smallest particle that can show all the 
phenomena of life?” In the case of the animal ovum as 
already noted this is about one-fourth of its volume, if we 
include development as one of the phenomena of life. Cer- 
tainly development includes all the phenomena of life. In the 
case of Stentor the volume is relatively considerably less as the 
following calculation will show: 
The volume of the smallest perfect Stentor polymorphus, 
which I was able to produce, was equal to that of a sphere of 
about 80 diameter; the average volume of the Stentors 
used in the experiments was equal to that of a sphere of 
about 230m, as I determined from a series of measurements of 
animals killed in a weak killing-fluid, and thus completely con- 
tracted. That is, the ratio of the diameters of the smallest 
and the average Stentor is about 1:3; or the ratio of volume 
to volume is about 1:27. That is to say that the smallest 
Stentor which can be produced is about one twenty-seventh of 
the volume of the average Stentor.! This number is of course 
a mere approximation, but it certainly will not be made any 
greater by subsequent investigation, though it may be lessened 
somewhat. 
8 In the case of S. coerudeus the figures are different: the smallest measurement 
which I have of this species is g0u; the average is 280u; thus the ratio of the 
smallest to the average is about 1:3 in terms of the diameter, or 1:27 in terms of 
volume. I believe, however, that it would be possible to produce a smaller S. 
coeruleus by working over a larger amount of material. I do not think that there 
is much difference in the absolute size of the smallest Stentors which can be pro- 
duced, whether one uses the largest or smallest normal specimens. If e.g. the 
average size of a lot of large Stentors were 320u, the smallest specimen which 
could be produced would still be 804. The ratio of volumes would then be 1:64. 
Of course this does not necessarily mean that 64 Stentors could theoretically 
be produced at one time from a single one, for I doubt that the nucleus could un- 
dergo that amount of division. 
