212 STUDIES IN GENERAL PHYSIOLOGY 



polyp. If a 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 poly}) 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. 1 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 



i WORTMANN, Botanische Zeitung (1887). 



