INITIATION OF DEVELOPMENT IN EGG OF ARBACIA. 



391 



Uninseminated eggs from this same lot exposed to hypertonic sea- 

 water gave only 17 per cent, membranes. Eggs a day old that 

 have been repeatedly washed never gave membranes with hyper- 

 tonic sea-water, though they were capable of responding to in- 

 semination with complete membrane separation. 



Immature eggs give no response to treatment with hypertonic 

 sea-water, as experiments early in June revealed. 



The best criterion, we may conclude, for the capacity of the eggs 

 to respond to treatment with hypertonic sea-water is their response 

 to insemination. Eggs from the same lots as those which, when 

 inseminated, rapidly lift off fine membranes everywhere equidis- 

 tant from the eggs with wide perivitelline spaces are the best for 

 hypertonic sea-water treatment. Eggs in the presence of blood, 

 stale eggs, and immature eggs, lift few or no fertilization mem- 

 branes. Such eggs yield poor or no results with hypertonic sea- 

 water. 



I pass now to the consideration of the type of cleavage and 

 plutei resulting from Arbacia eggs exposed to hypertonic sea- 

 water (20, 22, and 24 parts 2.y 2 M NaCl or KC1 plus 80, 78, and 

 76 parts sea-water, respectively, and sea-water of greater hyper- 

 tonicity). And I may say at the outset that the quality and per 

 cent, of membranes separated in hypertonic sea-water are indices 

 of cleavage and the production of plutei. The production of 

 cleavage and of surface-swimming plutei are of the best quality 

 and most numerous from those lots of eggs with best membranes, 

 provided, always, that the exposure is optimum. Data on this 

 point are summarized in Table II. 



TABLE II. 



PER CENT. OF CLEAVAGE AND OF PLUTEI FROM EGGS OF ARBACIA FOLLOWING 

 EXPOSURE TO HYPERTONIC SEA-WATER IN WHICH 

 THE EGGS SEPARATE MEMBRANES. 



