EARLY DETERMINATION IN DEVELOPMENT 

 UNDER NORMAL AND EXPERIMENTAL 

 CONDITIONS 



SILVIO RANZI: zoological department, 



THE UNIVERSITY OF MILAN, ITALY 



Development Alterations and How They Are Obtained 



Working on sea urchin embryos, Runnstrom (1954) and his 

 group showed that there are certain substances such as LiCl that 

 inhibit organ development at the animal half of the embryo by 



Fig. 

 1938.) 



1. Vegetalized sea urchin embryos. (From Lindahl and Ohman, 



inducing a developmental increase in the organs formed at the 

 vegetal half (vegetalized larvae) (Fig. 1). On the other hand, 

 other substances such as iodosobenzoate and NaSCN inhibit the 

 organs formed at the vegetal half and favor the development of 

 rudiments which appear at the animal half (animalized larvae) 

 ( Fig. 2 ) . The morphology of the two above mentioned larvae was 

 analyzed by Runnstrom ( 1928 ) , Lindahl ( 1936 ) , and Gustafson 



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