392 E. E. JUST. 



The experiments here cited, a fraction of the total, show that 

 the best cleavage and plutei, both as to quality and per cent., are 

 invariably found in those eggs that produce the best membranes. 

 At times the results are perfectly wonderful. Thus on August 9 

 eggs exposed the day before to KC1 hypertonic sea-water gave 

 gastrulse (and later plutei) that were scarcely to be distinguished 

 from those arising from normally fertilized eggs. The seven 

 dishes were simply alive with surface-swimming forms. These 

 eggs had lifted off very fine membranes. On the other hand, on 

 August 6 the eggs treated with KC1 hypertonic sea-v/ater lifted off 

 very poor membranes. They produced inferior cleavages and 

 larvae. The cleavage and larvse resulting from exposure to sea- 

 water of such concentration that membrane separation does not 

 take place in no wise compare to those from eggs in which mem- 

 brane separation takes place in hypertonic sea-water. 



In my experience insemination of eggs on return to normal sea- 

 water following an exposure to hypertonic sea-water that calls 

 forth membrane separation is not possible. If the cortical reac- 

 tion is complete and full membranes separate, insemination does 

 not increase the per cent, of cleavage and of plutei. In eggs 

 induced to form membranes by hypertonic sea-water the cortical 

 reaction is therefore complete and irreversible. 



The results here reported are in every way equal to those ob- 

 tained with the butyric acid-hypertonic sea-water method. In- 

 deed, in my experience the results with the use of the strong 

 hypertonic solutions have proved superior to the butyric acid- 

 hypertonic sea-water method. And certainly the use of hypertonic 

 sea-water alone is far more simple. With butyric acid one must 

 get just the right exposure for membrane separation. In any lot 

 of eggs, a mixed population, all eggs do not have precisely the 

 same optimum point of exposure to butyric acid for perfect mem- 

 branes. Moreover, even with the very highest per cent, of mem- 

 branes following butyric-acid treatment, the worker must again at 

 intervals give the eggs exposure to hypertonic sea-water of various 

 lengths. Three optima must the worker, therefore, obtain for best 

 results : optimum exposure to butyric acid, optimum length of time 

 in sea-water following butyric-acid treatment before exposure to 

 hypertonic sea-water, and optimum exposure to hypertonic sea- 



