DIFFERENTIAL SUSCEPTIBILITY IN POLYCHETES 3 



were used, either after staining with neutral red as an indicator 

 for death (Child, '16 b, '16 d) or without neutral red, or neutral 

 red was used after exposure to the agent for various periods, 

 and the results as regards the existence of axial differences in 

 susceptibility were essentially the same with all procedures, 

 though differences in the degree and character of protoplasmic 

 change appear with different agents. 



Chaetopterus 



Since it is evident from well known facts that in Chaetopterus 

 as well as the other species under consideration, the polar axis 

 of the egg after fertilization has not been determined during 

 fertilization, but must have been present in earlier stages, and, 

 since the susceptibility of the fertilized egg to the agents used 

 is higher and the axial gradient more distinct, little time has 

 been spent in demonstrating the polar gradient in the unfertilized 

 egg. 



In the unfertilized egg of Chaetopterus, however, a very dis- 

 tinct apico-basal susceptibility gradient has been observed, by 

 means of KNC m/100 after neutral red. The change of the 

 neutral red to yellow, as the protoplasm dies and the alkali of 

 the KNC solution penetrates the cytoplasm, and the following 

 decoloration begin at the apical or animal pole and progress 

 basipetally through the egg. After five to six hours in the solu- 

 tion most eggs show a beautiful color gradation from light yellow 

 or complete absence of the stain in the apical region to deep red 

 in the basal region, and after eight or nine hours the change is 

 usually complete. The color change is accompanied by an in- 

 creasing cytoplasmic translucency, and sometimes the membrane 

 is ruptured at some point, and the egg substance bursts out, 

 evidently under high pressure in consequence of a tendency to 

 swell in the solution. In such cases the cytoplasm disintegrates 

 and dies rapidly in the solution and the egg is of no further value 

 for demonstration of a gradient. 



In the fertilized egg of Chaetopterus before cleavage, swelling 

 and bursting occur very frequently in the higher concentrations 

 of KNC and alcohol, but where bursting does not occur, the 



