2o8 Echvin G. Conklin. 



matter of fact there is not the slightest indication in an anterior 

 half embryo of any attempt to restore the missing myoplasm or 

 muscle cells, nor does a posterior half embryo show any tendency 

 to form chorda-neuroplasm or neural plate or chorda cells. So 

 far as observation and experiment show, each ooplasmic substance 

 is capable of giving rise only to one particular kind of organ or 

 tissue. 



The question may be raised whether the presence of the injured 

 blastomere within the chorion may not influence the development 

 of the surviving cells and possibly prevent regeneration. In this 

 and in all previous experimental work on the ascidian egg these 

 injured cells have been left within the chorion in contact with the 

 surviving cells and in this respect all work on these eggs has been 

 done under similar conditions. Owing to the presence of the 

 chorion it is practically impossible to remove the injured cells, 

 and I am therefore unable to furnish an experimental test of the 

 influence or lack of influence of these cells upon the surviving ones. 

 However, there is suflBcient evidence, I think, to show that it is 

 not the presence of these cells which prevents regeneration. 

 Contact with the injured cell might be expected to hinder or pre- 

 vent the closing of the surviving half along the injured side, but it 

 is just this form of regulation, and this only, which is manifested 

 by these eggs. The presence of the injured cells can have nothing 

 to do with the failure of the anterior half embryo to form a tail, 

 or the posterior half embryo, a head; on the other hand, I have 

 shown conclusively that the development of a tail is dependent 

 upon the presence of a notochord, and the formation of a head 

 upon the presence of the gastral endoderm and neural plate. The 

 only possible influence of the injured cell upon the surviving one 

 would be to limit the form-regulation; but as I have said this it 

 does not do. It is inconceivable that the presence of the injured 

 cell should prevent the myoplasm from giving rise to other organs 

 than muscles, or the chorda-neuroplasm to other organs than 

 chorda and neural plate. 



These injured cells are rarely killed, but they remain transparent 

 and entire, although quiescent; they do not decay and form a nidus 

 for bacteria and I am convinced that their presence does not 

 materially influence the development of the surviving half nor 

 limit its powers of regulation. 



