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 in 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 stereotropie. 



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. 



3. 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. If a 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, ocellse are formed at both edges of the 

 wound. 



IV. If the entire brain of a Ciona intestinalis is extir- 



