VI 



ORGANIZATION AND GROWTH 1 



I. THE DEPENDENCE OF ORGANIZATION IN ANTENNULARIA 

 ANTENNINA UPON THE ORIENTATION OF THE ANIMAL 

 TOWARD THE CENTER OF THE EARTH 



1. THE 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 morphogeiietic 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 1-2 mm. in diameter and often 

 more than 2()cm. long, arises from a mass of roots W. 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 geotropisin; that is to say, the growing parts of 



'WQrzburg: Gcorg Hertz, 1891. Although dated 1W2, thi- pamphlrt appeared 

 in 1891. 



191 



