FERTILIZATION REACTION IN ECHINARACHNIUS PARMA. 5 



of buds at any time during the season is to allow the uninseminated 

 eggs to stand in a small quantity of sea-water in a shallow dish, 

 thus permitting evaporation; or, better, to place uninseminated 

 eggs in hypertonic sea-water (6 parts of 2^4 M NaCl plus 50 parts 

 sea-water). On transfer of the eggs to normal sea- water they are 

 gently shaken or squirted through a pipette. Large numbers of 

 such eggs produce buds. 



On insemination membranes separate from but one component 

 of these budded eggs. Only that portion of the egg within the 

 membrane divides and gastrulates. The gastrulse swim attached to 

 the undifferentiated mass of budded cytoplasm which eventually 

 disintegrates. The process of bud formation is easily followed 

 under the microscope and insemination made at any stage. In- 

 semination made after complete separation of the bud gives the 

 same result : in any two given masses of egg material separated by 

 constriction of a bud one only develops, regardless of size or the 

 presence of the egg nucleus. 



The explanation of these results on budded eggs of Echina- 

 rachnius is as follows : The cortex of the eggs changes under vari- 

 ous forms of treatment. As the uninseminated egg of Echinarach- 

 nius lies in sea-water it slowly deteriorates. A distinguishing 

 mark of this deterioration is the physical change in the cortex : the 

 cortex is thick and practically transparent. Late in the season also 

 many eggs are found with thick cortices. Blood, too, will fre- 

 quently hasten this change in the cortex. Now, hypertonic sea- 

 water very clearly brings about a physical change in the cortex. 

 After exposure to hypertonic sea-water the cortex may be readily 

 seen as a thick jelly-like hull enclosing the egg. It is from this 

 jellied cortex that the membrane separates on insemination. 



If an egg with a thick cortex be gently shaken on transferal to 

 normal sea-water, the cortex breaks and the contents of the egg 

 flows out. Indeed, merely the transfer from hypertonic sea-water 

 to normal sea-water will tend to produce this outflow in some eggs, 

 as they rapidly take up water. The bud is thus made up of endo- 

 plasm and is without cortical material. In favorable cases this is 

 readily determined. 



And only that component of the budded egg which has the clear 

 rim of cortex is fertilized on insemination as revealed by the pres- 



