ORGANIZATION AND GROWTH 241 
through. I inserted into the tube a Tubularian from which I 
had previously cut off the root and polyp, so that the one 
end 6 was in the tube and the other end c was freely sur- 
rounded by water in the aquarium. A polyp was formed 
nearly always upon the free end c¢, but only exceptionally 
upon the end b in the tube. The oxygen dis- 
solved in the water within the glass tube did 
not suffice to render regeneration possible at 
the end b. is 
That regeneration only was inhibited, while 
the power of regeneration was preserved, is 
evidenced by the fact that if, after not too 
long a time, I brought the end b back into b 
fresh sea-water, regeneration occurred. 
This also explains some of the facts mentioned 
in paper iv (Part I, pp. 123 and 124). I 
mentioned that when one end of a Tubularian 
is fixed in the sand, or in a narrow cleft between 
two slides, no regeneration occurs at this end 
(even though death does not occur—at least for some time). 
At that time I was inclined to attribute the result to mechan- 
ical factors (pressure), but I believe now that we were prob- 
ably dealing with lack of oxygen. 
When I suspended Tubularie in the aquarium in such a 
way that the one end was very close to the surface of the 
sand, but did not touch it, and arranged my apparatus so 
that only a small current of water entered the surface of the 
aquarium, and kept the whole free from movement, no 
regeneration followed at this end. The cause for this is as 
above. According to Jacobsen, the layer of water just above 
the mud bottom of the ocean is poor in oxygen.’ 
It may be that a movement of protoplasm toward the end 
of a stem is possible only when this cut end is contained in 
1 JACOBSEN, Annalen der Chemie und Pharmazie, Vol. CLXVII (1873). 
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