THIRD LECTURE. 



ON SOME FACTS AND PRINCIPLES OF PHYSIO- 

 LOGICAL MORPHOLOGY. 



JACQUES LOEB. 



IN this address I shall give a short account of a series of 

 experiments which were undertaken in order to 

 determine the causes of animal forms. Some of 

 the results of these investigations have already 

 been published. 1 Among others, which are new, 

 are experiments upon the artificial production of 

 double and multiple monstrosities from one ovum 

 in the sea-urchin. 



I. HETEROMORPHOSIS. 



If we look at an animal we perceive that its 

 various organs are arranged in a definite way, 

 From our shoulders originate arms, and from our 

 hips legs, but we never see that legs grow out 

 from the shoulders or arms from the hips. In 

 the lower animals there exists the same definite 

 arrangement of parts. 



Fig. i is a diagram of a hydroid Antennularia, 

 which is pretty common at Naples. From a 

 bundle of roots or stolons a perfectly straight 

 stem arises to a height of six inches or more. 

 From this main stem originate, in regular suc- 

 cession, very short and slender branches, which 

 carry polyps on their upper sides. 



In this case we never find that a root originates 

 at the apex, or in the place of a branch, or that 

 polyps originate at the lower side of a branch. To the 



1 Untersuckungen znr pkysiologiscke* Morphologic der Thiere. I, Heteromor- 

 phosis, Wiirzburg, 1891. II, Organbildung und Wachsthum, Wiirzburg, 1892. 



