FERTILIZATION REACTION IN ECHINARACHNIUS PARMA. 3 



in size (through absorption of water) and flow together into 

 larger drops. This goes on until finally the contents of all the 

 drops have run together into a continuous layer around the egg. 

 Hence the surface lamellae of the tiny droplets form later the 

 fertilization membrane." At higher temperatures, the egg of 

 Strongylocentrotus forms a membrane very quickly passing directly 

 from the. condition of the uninseminated egg to that with fully 

 formed membrane and wide perivitelline space; thus too in 

 Arbacia. (Loeb, loc. cit.} 



During a study of the fertilization reaction in the egg of 

 Echinaracknius covering several seasons at the Marine Biological 

 Laboratory at Woods Hole, Mass., I have made observations on 

 membrane elevation in this egg where the process though it 

 takes place with great rapidity can nevertheless because of the 

 size of the egg be followed with remarkable ease. I can, there- 

 fore, make the unqualified statement that in the egg of Echi- 

 narachnius membrane elevation proceeds as a wave from the 

 entrance-point of the sperm around the cortex. Moreover, 

 what is more significant, before membrane elevation cortical 

 changes blocking farther sperm entry spread as a wave over the 

 egg uniting finally at the point opposite the entrance-point of 

 the sperm. 



OBSERVATIONS. 1 



If eggs of Echinarachnius be inseminated with thin sperm sus- 

 pension they throw off membranes that are fully formed and 

 equidistant from the surface of the vitellus in from two to three 

 minutes. This follows sperm penetration which may take place 

 at any point. Sperm is engulfed by the egg in from fourteen to 

 forty-five seconds after insemination; the membrane begins to 

 lift off in from seven to twenty-two seconds after sperm entry is 

 complete; and membrane elevation is complete in from nine to 

 thirty seconds after it begins. The shortest time recorded from 

 insemination to membrane elevation from all parts of the egg is 

 thirty-nine seconds, all time being taken with a stop-watch of a 



1 All observations were made on eggs in a quantity of sea-water; the eggs never 

 suffered compression. Though jelly-free eggs form membranes, most observations 

 were made on eggs with jelly so that the eggs were therefore free from flattening 

 when on the bottom of the dish the jelly acting as a buffer. Flattening of the 

 eggs might easily lead to erroneous conclusions. 



