ON SOME FACTS AND PRINCIPLES OF PHYSIOLOGICAL 



MORPHOLOGY ^ 



I. HETEROMORPHOSIS- 



The various organs of the higher animals have a definite 

 arrangement; from the shoulders arms originate, from the hips 

 legs, but we never see legs growing out from the shoulders 

 or arms from the hips. In the lower animals the same definite 

 arrangement of organs exists. 



Fig. 22 gives a diagram of a hydroid, Antennularia anten- 

 nina, which is quite common in the Bay of Naples. From a 

 bundle of roots or stolons a straight stem arises to a height of 

 six inches or more. From this main stem originate, in regular 

 succession, short and slender branches, which carry polyps on 

 their upper sides. 



In this animal we never find a root originating at the apex, 

 or in place of a branch, or polyps originating on the under side 

 of a branch. 



In observing these phenomena the question arose : What are 

 the circumstances which determine that only one kind of organ 

 shall originate at certain places in the body? It occurred to 

 me that the answer to this question might be obtained by finding 

 out first of all whether or not it were possible to make any 

 desired organ of an animal grow at any desired place. In case 

 this could be done, the question to be decided was whether the 

 same circumstances by which the arrangement of organs can 

 be changed experimentally also determine the arrangement of 



1 Reprinted from Biological Lectvires delivered at the Marine Biological 

 Laboratory of Woods Hole, 1893. by courtesy of Ginn & Co. 



2 Untersuchungen zur physiologischen Morphologie der Tiere. I, Hetero- 

 morphosis, Wtirzburg, 1891. II. Organbildung und AVachsthum. Wurzburg, 1892. 

 Translated in Studies in General Physiology. 



85 



