130 STUDIES IN GENERAL PHYSIOLOGY 



specimens, to select only those which are very thin at the 

 base. Such a selection might easily be made accidentally in 

 an experiment. In this case one might notice that polyps 

 arise only at the oral end, especially if the experiments are 

 not continued for a very long time. Just as Allman regards 

 such a behavior as the expression of polarity in the animal 

 body, some botanists speak in analogous cases of " mor- 

 phological forces." I believe that the "morphological 

 force" which decides that a polyp forms first at the oral 

 end of a Tubularian segment is essentially nothing more 

 than that the diameter of the tube is very small at the 

 aboral end of the stem. Yet I prefer not to enter into 

 a discussion of such hypothetical things in this paper. 



V. HETEROMORPHOSIS IN AGLAOPHENIA PLUMA 



While in Tubularia we dealt with but a single stem which 

 under ordinary conditions ends in a root at one end and in a 

 polyp at the other, we have to deal in what follows with 

 colonies of animals. The place of the head is here taken 

 by a more or less ramified stem possessing many polyps. 

 At the other end is formed a root (as in Tubularia). We 

 shall confine ourselves to experiments upon the stems. 

 We shall call the end directed toward the root the aboral 

 or basal end of the animal; the other, free end, the oral 

 or apical end. I wished to determine whether it was pos- 

 sible to make a new tip grow in place of the root at the 

 basal end of the stem, or vice versa, and how we might 

 accomplish this. 



1. Aglaophenia pluma (see Figs. 17-19) consists of a 

 main stem from which lateral branches are given off on both 

 sides. These side branches carry polyps upon their upper 

 surfaces ; they are slightly convex toward the tip of the main 

 stem and arise from it at an acute angle, which opens toward 

 the tip of the main stem. The side branches are the shorter 



