ORGANIZATION AND GROWTH 223 
from vegetable protoplasm. If a Tubularian stem is trans- 
ferred from pure sea-water to sea-water that has been diluted 
by the addition of distilled water, water must enter the cells, 
and these must in consequence become more turgid. On 
the other hand, if the Tubularian is placed in sea-water, the 
concentration of which has been raised through evaporation, 
the absorption of water by the animal must fall below the 
normal, and water must finally pass from the cells into the 
solution. The following experiments show how changes in 
the concentration of the sea-water affect regeneration. The 
temperature in all these experiments varied between 12° and 
15° C., and was always the same for the same series of ex- 
periments. The number of animals in the individual dishes 
of the same series of experiments was also nearly equal; 
every dish contained 300 c.c. of sea-water. 
2. I distributed a large number of fresh, healthy stems 
of the same colony of Tubularia into three salt solutions. 
The first of these consisted of sea-water to which 332 per 
cent. of its volume of distilled water had been added; the 
second, of ordinary sea-water; and the third, of sea-water 
which had been evaporated to 75 per cent. of its volume. In 
order to have all the solutions exactly alike except in con- 
centration, the two former were heated to the boiling-point, 
filtered, and, like the third, shaken for some time in the air. 
After two days nine of the twelve stems in the dilute sea- 
water had regenerated the polyps which they had lost; in 
the normal sea-water only six of the sixteen stems had 
regenerated; in the concentrated sea-water regeneration had 
not taken place in a single stem. Six hours later regenera- 
tion was complete in all the Tubularians in the dilute sea- 
water, and on the following day this was also the case in the 
ordinary sea-water. Three days later a change occurred at 
the cut end of one of the animals in the concentrated salt 
solution which looked like a beginning of regeneration, but it 
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