A STUDY OF THE DIFFERENTIATION OF NEURO- 

 BLASTS IN ARTIFICIAL CULTURE MEDIA' 



MARIAN L. SHOREY 



Milwaukee- Downer College 



TEN FIGURES 



Few biological problems offer greater difficulties than those 

 that attempt to deal concretely with the factors involved in the 

 process of differentiation. In the light of our present knowledge, 

 as well as on purely a priori grounds, the two extreme views, that 

 of Driesch and his followers, that ''the prospective value of a 

 blastomere is a function of its position," and the mosaic theory 

 in its most pronounced form, that development " is to be regarded 

 as a mosaic work of self-differentiating cells,"- seem equally 

 untenable. The work of numerous investigators on a great variety 

 of forms has established beyond question that when certain ooplas- 

 mic substances are destroyed the tissues into which they normally 

 develop are lacking. On the other hand the fact that develop- 

 ment may proceed for a time after the destruction of portions of 

 the organism does not, for many reasons, demonstrate that the 

 remaining portions are in any degree self-differentiating. First 

 of all it is noticeable that development after the injury depends 

 not so much on the extent as on the character of the substances 

 destroyed. For example, Conklin,^ in the study of ascidian eggs, 

 found that a right or left half embyro develops much farther and 

 much more normally than an anterior or posterior half, and from 



' I wish to express my indebtedness to Professor F. R. Lillie, Director of the 

 Wood's Hole Marine Biological Laboratory, and to Professor S. J. Holmes, of the 

 University of Wisconsin, for many courtesies received at the two institutions 

 named while this paper was in preparation. 



2 Wilson, E. B., '04. Mosaic Development in the Annelid Egg. Science, vol. 20. 



' Conklin, E. G., '05. Mosaic Development in Ascidian Eggs. Jour. Exp. ZooL, 

 vol. 2. 



