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Chas. B. Wilson- 



pigment cells, but must be attributed to the sluggishness of the 

 yolk cells. This is another evidence in favor of the view that even 

 at an advanced stage in the formation of the blastopore, the with- 

 drawal of the yolk cells is the first requisite for the completion of 

 that formation, and the yolk cells are themselves the active agents 

 of their own withdrawal. 



It would be suggested also that ordinarily these yolk cells 

 contain just about enough active protoplasm scattered amongst their 

 yolk granules to accomplish such a withdrawal. The influence of 

 the salt solution weakens the activity of this protoplasm, and thus 

 renders the withdrawal impossible for the time being. Subsequently 

 this activity may recover from the influence of the solution, and 

 increase until it is sufficient to move the yolk cells. 



Such an adaptation of vital functions to altered conditions is 

 by no means rare. 



It may be said that something of the sort always occurs when 

 the change in conditions is not sufficient to overcome the function 

 altogether. If the change be comparatively small, as in the present 

 instance, the organism may be able to recover completely, and re- 

 sume its normal functions. 



This is shown more clearly in Experiment 12. The remainder 

 of these eggs were allowed to develop normally for four days before 

 being placed in the solution. 



In this time they had reached an advanced stage, the blastopore 

 being closed, the body elongated, and the anterior and posterior 

 ends well developed. The solution produced no visible external 

 change in their further growth, but they all weakened and died 

 within five days. 



We have thus subjected Kana eggs in different stages of deve- 

 lopment to the influence of both salt and Einger solutions. 



We find that eggs which have already begun to segment always 

 lie dormant for a time on being placed in the solution. 



The first influence of either solution is like that of a low 

 temperature and results in a complete checking or temporary para- 

 lysis of the vital activities. The eggs recover and go on developing 

 after a period which varies with the amount of segmentation which 

 they have undergone previous to being placed in the solution; the 

 more advanced the segmentation the longer the period of rest. 



Subjection to either solution at a late stage of segmentation is 

 also more likely to prove fatal. After developing normally for a 



