Selected Invertebrates 



333 



above). Up to 6 hours after fertilization such 

 detergents prevent development of the oral 

 (ventral) side and radial symmetry results; 

 but between 6 and 9 hours after fertilization 

 the detergents gradually lose their effects 

 and after 9 hours they can no longer inhibit 

 development of bilaterality. 



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