EXPERIMENTAL CONTROL AND MODIFICATION OF 



LARVAL DEVELOPMENT IN THE SEA URCHIN 



IN RELATION TO THE AXIAL GRADIENTS 



C. M. CHILD 

 Hull Zoological Laboratory, University of Chicago ] 



EIGHT PLATES ' 



) 



The literature of experimental teratogeny in embryonic and 

 larval development is extensive and a great variety of external 

 factors has been employed in experimentation along this line. 

 While the results have often been of great interest, no general 

 basis for interpretation has been reached, particularly as re- 

 gards the relation between teratological form and the action of 

 experimental factors to which the developing organism is sub- 

 jected as a whole, and not by local application. It is a familiar 

 fact that even such factors affect different regions or parts difr 

 ferently or to a different degree, and while such differences indi- 

 cate the existence of local differences of some sort, there is, in 

 general, a very evident lack of specificity in the action of differ- 

 ent external factors on the course of organic development. Simi- 

 lar teratological forms may often be produced by many different 

 agents and conditions. 



The present paper constitutes one step in the attempt to cor- 

 relate certain types of teratological development with dynamic 

 conditions which are characteristic and fundamental features of 

 the normal organism. It establishes a basis for the control, 

 modification and prediction of the course of development in the 

 sea urchin, and the facts already at hand indicate very clearly 

 that certain types of teratological development, as well as cer- 

 tain characteristic features of normal development, can readify 

 be interpreted on the same basis. More specifically this paper 

 is a demonstration of the effectiveness of the axial metabolic 

 gradients as dynamic factors in the development of the sea 



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JOURNAL OF MORPHOLOGY, VOL. 28, NO. 1 



