628 STUDIES IN GENERAL PHYSIOLOGY 
with the optic ganglion be removed, an antenna will be 
produced in the place of the eye, while if the eye alone 
is cut off an eye is regenerated. The presence or absence of 
the optic ganglion decides whether a regeneration or a hetero- 
morphosis will follow.’ 
I found, very early in my experiments, that in certain 
Hydroids a heteromorphosis can be produced without any 
organ being cut off or any wound being inflicted upon the 
animal. In Antennularia—a Hydroid common at Naples— 
the arrangement and orientation of the organ as well as 
the direction of growth is dominated by gravitation. The 
animal consists of a straight vertical stem, which forms 
stolons at its lower end and which carries small branches 
with limited growth at regular intervals. On the upper 
surface of these branches the polyps are found. If such a 
stem be suspended horizontally in the water the lateral 
branches which are directed downward and which had 
finished growing now begin to grow downward very rapidly. 
At the same time the polyps on these branches disappear. 
The downward-growing parts no longer resemble the old 
side-branches but look like roots. A closer examination 
reveals the fact that they not only possess the morphological 
appearance of roots but also the physiological reactions of the 
latter, inasmuch as they are positively geotropic and stereo- 
tropic, while the branches do not show these forms of 
irritability. In this case the tissue of the polyps which dis- 
appeared seems to have been transformed into the tissue of 
roots.” 
I made a similar observation shortly afterwards at Woods 
Hole in another Hydroid, Margelis. When the uninjured 
points of a stem of Margelis are brought in contact with a 
solid body the point of the stem assumes the form and 
1 Hersst, Archiv fiir Entwickelungsmechanik, Vol. IX (1899), p. 215. 
2 Part I, p.191. 
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