414 ^- J- Holmes 



istic pushing ahead of the oral side did not occur. The aboral 

 side in fact began to be pushed ahead of the oral which accounts 

 for the form of the pieces shown in the figures. After several 

 hours the oral margin became thinner and clearer and the gran- 

 ules of the endoplasm came to lie further from the edge. A slight 

 transverse striation could be detected in it such as occurs more 

 plainly in the normal individual, and soon short cilia began to be 

 put out here and there chiefly toward the posterior end. As the 

 clear margin became broader it showed a longitudinal striation 

 and soon began to extend and contract more during the move- 

 ments of the body. As the oral margin slowly acquired its char- 

 acteristic differentiation it began to push ahead and extend around 

 the anterior end where its striations assumed the usual bend. 



Fig. 5 Regeneration of a piece from the middle of the body from which the oral margin was removed. 



In this case regeneration was very slow compared with the tw^o 

 preceding experiments. The piece was larger in size than the 

 others but more differentiation had to be accomplished. Not until 

 the oral margin became furnished with its cilia and its differ- 

 entiated contractile elements so that it was capable of performing 

 its usual role in the movements of the animal was there any marked 

 progress in molding the body into its final shape. The anterior 

 end, although it had become narrowed and rounded soon after the 

 operation, did not take on any of its characteristic structural 

 features until the oral margin became differentiated and began to 

 be stretched around the front as in the cases of regeneration just 

 described. 



The development of the new cilia extended gradually forward 

 from the small part of the ciliated margin that remained and the 



