ACTION OF VISIBLE RAYS ON ARBACIA EGGS. 3 



3. "Where the effect of differential inhibition persists after 

 general recovery, a great over-development of the skeleton may 

 occur, since the mesenchyme cells are relatively less inhibited 

 than most, if not all other parts." 



Larva? whose development has been modified by means of 

 radiation, present exactly the same picture as those produced by 

 other means. 



Method. In general, in experiments in which differential 

 inhibition has been produced, the method has been as follows: 

 The eggs from a single female were strained through a cheese- 

 cloth and washed. They were then stained in weak sea-water 

 solutions of one or the other of the above dyes, for from ten to 

 thirty minutes, again washed and then exposed for varying 

 periods of time to radiation from one of the above-mentioned 

 sources of light. (In some cases the eggs were exposed in a thin 

 layer of a weak concentration of the dye.) Eggs were then 

 washed and returned to sea-water and allowed to develop in the 

 dark. The experimental controls consisted of (-4) stained and 

 unstained eggs (unexposed to strong light) which were allowed to 

 develop in diffuse daylight, and another similar lot which de- 

 veloped in the dark, and (B) unstained eggs (exposed to strong 

 light) and allowed to develop in the dark. Temperature was 

 controlled by the addition of ice to the water bath surrounding 

 the eggs. 



Differential recovery followed in those cases where the inhi- 

 bition was only transitory. Differential acclimation was ob- 

 tained by allowing fertilized eggs to develop in sea-water solutions 

 of dyes exposed to diffuse daylight. 



Results. Results of experiments made during the summers of 

 1923 and 1924 may be tabulated as follows: 



A. Differential inhibition no recovery. 



B. Differential inhibition differential recovery. 



C. Differential inhibition general recovery. 



D. Differential acclimation. 



A. Differential Inhibition. Since it is true that those regions 

 which are relatively the most active physiologically, during a 

 particular stage of growth, are also the most highly susceptible 

 to the destructive action of lethal doses of chemical agents 



