INTRODUCTION 



It was in 1903, 58 years ago, that I, then a young man who had 

 just left the classical grammar school at Zagreb, went to Vienna 

 to study Natural Sciences and above all my beloved Zoology 

 at Vienna University. For this study I was well prepared. Whilst 

 at school, I had made a large collection of zoological objects. 

 I had learnt the richness of forms and the ways of life of the 

 animal world through my diligent study of Brehm's work on 

 the Lives of Animals as well as through my field studies. At 

 Vienna my teachers were the two professors of zoology, Carl 

 Grobben and Berthold Hatschek, particularly the latter under 

 whose guidance I also worked on my dissertation thesis. 



During my second year at university, a pubUc aquarium was 

 purchased in Prater by some young Austrian biologists support- 

 ed by their prosperous parents; in it they established a modern 

 biological research institute— The Prater Biological Experi- 

 mental Testing Station (Die biologische Versuchsanstalt im 

 Prater)— and I applied as one of the first to this place to learn 

 there the methods of scientific research. Dr. Hans Przibram, 

 then Privatdocent, was the head of the department; he is the 

 author of the well known synoptic work on Experimental 

 Zoology. Hydra was my first object of study. There were nu- 

 merous green Hjdm in a half-darkened concrete basin; their 

 exterior looked rather pale. This induced me to transfer the 

 same Hjdra into a completely darkened place. When these 

 hijdra began to procreate I could observe what I had actually 

 expected: their ova were without the symbiotic green algae 

 so that finally there w^ere at least some colourless '' green" Hjdra . 

 Other tests and researches w^ere made in the same place. In 

 1906 my first results were published in Roux's Archiv fiir Ent- 

 mcklungsmechanik . 



