12 C. M. CHILD 



stain at once when the ectoderm is torn open or partly removed, 

 as well as when the ectoderm is approaching death, it is evident 

 that their slow staining or failure to stain in normal animals 

 after complete overgrowth by ectoderm is due simply to the storing 

 up in some way of the neutral red in the ectoderm cells as rapidly 

 or almost as rapidly as it enters. As the action of the toxic 

 agent progresses, the ectoderm cells become less and less able to 

 hold neutral red, and the neutral red which enters them passes 

 through and enters the macromeres, which are as yet but little 

 or not at all affected by the killing agent. 



These same relations may be shown by still another modification 

 of procedure. The young larvae are first stained, for instance, the 

 ectoderm is stained, but little or no neutral red reaches the in- 

 closed macromeres, and then, after washing, the larvae are placed 

 in the killing agent without any admixture of neutral red. As the 

 ectoderm cells approach death they begin to give up their neutral 

 red, and at least a part of it passes to the macromeres which 

 stain more and more deeply until, finally, the ectoderm is dead 

 and decolorized, and the entoderm deeply stained. The change 

 in relative physiological condition of ectoderm and entoderm 

 has evidently determined the redistribution of the neutral red. 

 Later, of course, the entoderm also undergoes decoloration, but, 

 whether it is directly exposed to the action of the toxic agent 

 or inclosed in ectoderm, its susceptibility is very much lower 

 than that of the ectoderm. 



The behavior of the trochoblasts and the prototroch is of 

 interest. So far as I have been able to determine, the trocho- 

 blasts, when first formed, do not show any marked differences 

 in susceptibility from adjoining cells. This suceptibility, like 

 that of other cells of the more apical portions of the egg is high. 

 At the time ciliation develops, and perhaps for some time after, 

 the cells of the prototroch are apparently the most susceptible 

 cells of the apical hemisphere, and when eggs are placed soon 

 after fertilization in concentrations of KNC low enough to permit 

 development to progress slowly as far as the early trochophore 

 stage, but not low enough to permit acclimation (for example 

 w/25000andin some cases m/50000), the cells of the prototroch 



