396 



C. M. CHILD. 



are in a sense only preliminary, although of course essential to 

 the fundamental processes of life and the relation between 

 susceptibility and metabolic rate is primarily concerned, not 

 with them, but rather with the reactions which play a funda- 

 mental role in setting free the energy characteristic of living 

 organisms. 



In the sea urchin the differences in susceptibility along the 

 axis so far as observed, are essentially the same whether cyanides, 

 alcohol, alkalies or acids are used as reagents. All these sub- 

 stances interfere with the action of the protoplasmic system in 

 some way, but by no means necessarily in the same way, yet 

 the general results as regards susceptibility are the same. This 

 fact is highly significant and indicates to some extent the general 

 character of the relation between susceptibility and the funda- 

 mental conditions and processes of life. 



THE EGGS AND CLEAVAGE STAGES. 



Since experiments on the control and modification of develop- 

 ment through differential susceptibility along the axes had shown 

 very conclusively the existence of axial gradients in the early de- 

 velopmental stages and had indicated their probable presence even 

 in the unfertilized egg, and since it was soon found that the 

 character of the death changes made it difficult to reach definite 

 conclusions concerning death gradients from direct observation, 

 but little time was spent on these earlier stages and the evidence 

 obtained, so far as it has any value, is merely contributory. 

 I regret to state, however, that I neglected to employ as a means 

 of orientation the method of making the micropyle visible by 

 colored suspensions in the water. This might have made the 

 data on these earlier stages somewhat more conclusive. 



