ORGANIZATION AND GROWTH 251 
appearance in no way from the old oral plate. A slight swelling of 
the body-wall showed the position of the original cut iu this double 
polyp. The position of the latter also showed that the body itself 
had grown aborally. 
XVI. SUMMARY OF THE MORE IMPORTANT RESULTS 
I. The orientation of organs and the place where they 
originate can be controlled in Antennularia antennina at will 
through the following circumstances: 
1. The stems are negatively, the roots positively, geo- 
tropic and positively stereotropic. 
2. The place where the organs form is determined by the 
orientation of the animal toward the center of the earth, so 
that branches arise only on the upper surface of a stem; or, if 
the latter is in an absolutely vertical position, only from that 
cut end which is directed upward. The opposite holds for 
the roots, with this addition, however, that in the region 
where new stems originate new roots may at times also be 
formed upon the upper surface of the old stem. 
8. If a growing but uninjured stem of Antennularia 
antennina is suspended with its tip downward, the stem 
ceases to grow as such, but roots may arise from the tip. 
4, When a stem is placed horizontally or-obliquely, the 
branches which are directed downward may grow as roots, 
even when they are not injured and not in contact with solid 
bodies. 
II. Ifa piece is cut from the stem of a Tubularian, the 
regeneration of the polyp at the oral end may retard the for- 
mation of a polyp at the other. By suppressing the for- 
mation of the oral polyp one can accelerate considerably the 
formation of the polyp at the aboral end. 
III. If an incision is made into one of the tubes of a 
Ciona intestinalis, ocelle are formed at both edges of the 
wound. 
IV. If the entire brain of a Ciona intestinalis is extir- 
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