212 STUDIES IN GENERAL PHYSIOLOGY 
polyp. Ifa Tubularian stem is examined immediately after 
the polyp has been cut off, separate red pigment granules are 
found distributed quite regularly throughout the stem. On 
the following day a denser aggregation of these granules is 
observed in the vicinity of the cut ends, and after two or 
three days they are often so numerous that the cut end 
seems saturated with red. Soon thereafter the polyp is 
formed into which the red granules are collected. This 
occurs also in the formation of a polyp at the aboral end. 
I will not, of course, assert that these pigment granules are 
the formative substances of the polyps in the sense of Sachs’s 
hypothesis. It is rather to be assumed that, since pigment 
granules have no active motion, movements probably occur 
in the protoplasm of the Tubularian stem, at first in the 
direction from the aboral end to the oral, and later, when the 
oral polyp has been formed, in the reverse direction. It 
might also be that in some cases in which external stimuli 
have an influence upon organization these stimuli bring 
about or modify such protoplasmic streaming. The move- 
ment of protoplasm in plants under the influence of.external 
stimuli has been observed directly by Wortmann.’ The 
migration of the pigment granules toward the cut ends 
actually observed, and the connection between this migration 
and the formation of polyps, probably indicate that one is 
justified in believing that organization in Tubularia—and 
also other animals—is associated with the migration of 
formative substances. 
7. For the time being we may, therefore, believe that a 
heteromorphosis can be brought about whenever the specific 
formative substances can wander in different directions in 
the animal body; while in the case of animals possessing 
“polarity” this migration is possible in only one direction. 
When heteromorphosis occurs in Tubularia, but the oral 
1WorTMANN, Botanische Zeitung (1887). 
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