242 LILLTE: [Vor. XII. 
offer conditions for decision between these two alternatives. 
If it should be shown that a nucleated portion of the body 
below a certain minimal size is incapable of regeneration, the 
first alternative would receive support. If, on the other hand, 
the smallest nucleated fragments of the body are capable of 
regeneration with restoration of the normal form, the first 
hypothesis would fall, and the second tend to be established. 
My material consisted of two species of Stentor, viz.: S. 
polymorphus and S. coeruleus. The former species occurred in: 
immense profusion on decaying leaves of the water-lily in a 
small pond near Ann Arbor, the latter appeared in considerable 
numbers in a small aquarium which had stood in the laboratory 
for six or seven weeks, and contained gatherings from a swamp. 
This species is more favorable for experimental work than the 
former, because the protoplasm is transparent, enabling one to 
see the nucleus readily in the living animal. In S. jpoly- 
morphus the body is rendered almost perfectly opaque by the 
presence of immense numbers of symbiotic unicellular Algae, 
the so-called zoochlorellae, which either hide the nucleus com- 
pletely from view, or permit mere momentary glimpses of it. 
On account of the ease of procuring any desired supply of S. 
polymorphus my work was done chiefly on this form; but the 
results were checked on S. coeruleus, and were practically the 
same for both species. 
To reach the desired result it was necessary to find or devise 
a method by which nucleated fragments of every possible size, 
beginning with a portion not much larger than a single node 
of the nucleus, could be produced in large numbers; for 
reliable quantitative results can be reached only by observation 
of a large number of cases of regeneration. For this purpose 
I tried the method of shaking which has yielded such admir- 
able results with the animal ovum in the hands of Wilson, 
Driesch, Morgan, and others, and found it to succeed to per- 
fection. Ifa number of Stentors are put in a small vial about 
one-third filled with water and shaken quite violently from five 
to twenty times (S. coesnuleus requires to be shaken only about 
five times; SS. polymorphus ten to twenty times), and then 
examined under a low power of the microscope, one sees that 
