INITIATION OF DEVELOPMENT IN CILETOPTI kl S. 65 



stimulus of the same sort as that which initiated the development 

 could no longer be effective. Duplicating the first stimulus 

 would do no good. The time for the effective application of 

 potassium chloride had passed. A stimulus of a different sort 

 was needed. 



When the action of the one agent supplements that of the 

 other, however, the success of the experiment is increased. For 

 example, potass urn chloride added to heat reduced the percentage 

 of segmented swimmers below the record for heat alone, but it 

 increased the percentage of unsegmented swimmers above that 

 for potassium chloride alone. As will be recalled, potassium 

 chloride alone does not induce cleavage, but heat does do so. In 

 this case, then, it is evident that heat is the better agent, since 

 it induces a more normal result. It seems probable that the 

 reactions brought about by the potassium chloride are incomplete 

 in some way. Therefore when the two are applied together the 

 effect of the potassium chloride is heightened, because some of 

 the incomplete reactions are completed or supplied by the heat, 

 whereas the heat effect is lessened because its working is fairly 

 complete in itself, and is only injured by duplicating. 



SUMMARY OF DISCUSSION. 



It is quite impossible in the present state of uncertain knowl- 

 edge with regard to physiological causes and effects, as well as in 

 view of the small number of the experiments brought forward in 

 this paper, to draw any definitive conclusions as to the causes 

 of the initiation of development in Chcetoptenis. I should like 

 merely to summarize certain suggestions which seem to me most 

 in line with the findings. 



1. The great variety of agents which will induce the develop- 

 ment of Chcetoptems eggs indicates that the egg is in a very labile 

 state of equilibrium, and that the same results may be reached 

 by different processes. 



2. Development may be resolved into a separable series of 

 steps. A graded series of stimuli can be determined by which 

 development may be made to stop at almost any step in the 

 process. 



3. The cortical changes which accompany membrane formation 



