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 longtime. 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 ina 
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 
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