VI 
ORGANIZATION AND GROWTH! 
I, THE DEPENDENCE OF ORGANIZATION IN ANTENNULARIA 
ANTENNINA UPON THE ORIENTATION OF THE ANIMAL 
TOWARD THE CENTER OF THE EARTH 
1. Tue difference between physiological morphology and 
the purely descriptive morphology lies in this, that the for- 
mer endeavors to control the formation of organs. Its aim 
is, therefore, primarily a technical one. Since almost every- 
thing is still to be done in this direction, at present those 
cases will be especially welcome in which the means of con- 
trol of the morphogenetic processes are very simple and yet 
perfect. I have found that in Antennularia antennina, a 
Hydroid, it is possible to control the morphogenetic process 
with the aid of the position given it with reference to the 
center of the earth. By this means we can not only at will 
cause another organ to grow in the place of an amputated 
one, but we can compel an uninjured existing organ to stop 
growing in its old form and form an entirely different organ. 
2. In Antennularia antennina (Fig. 37) a straight 
unbranched stem SS, about 1-2mm. in diameter and often 
more than 20cm. long, arises from a mass of rootsW. Deli- 
cate lateral branches of limited growth and directed slightly 
upward spring from the stem in regular order. Upon the 
upper surface of these are polyps and nematophores, which 
are indicated only by points in the drawing. In order to 
save room, only the lower third of the stem has been drawn. 
I have previously pointed out that Antennularians show 
a decided geotropism; that is to say, the growing parts of 
1 Wurzburg: Georg Hertz, 1891. Although dated 1892, this pamphlet appeared 
in 1891, 
191 
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