GENERAL PROPERTIES OF THE ECTOPLASM 



separation and the egg is thereby so profoundly altered 

 that the normal processes of gastrulation are disturbed. 



The unfertilized eggs of Nereis limbata withstand treat- 

 ment with tap or distilled water for three or four minutes 

 before disintegration takes place. Beginning twenty-five 

 minutes after fertilization, the eggs are even more resistant 

 than the unfertilized. But during the twenty-five minute 

 period immediately following the mixing of eggs and sperma- 

 tozoa, the eggs show a very low resistance for they dis- 

 integrate within ten to sixty seconds after exposure to tap 

 or distilled water. The surface-changes described above 

 for this Q^^ run over this period of twenty-five minutes. 

 Thus, the period of susceptibility to hypotonicity exactly 

 coincides with the period of break-down of material in the 

 ectoplasm — with release of the jelly-forming material — the 

 amoeboid changes and the darkening of the egg. When the 

 &%% rounds up and clears, the period of lowered resistance 

 to dilute sea-water passes oflf. 



These experimental findings on three forms— and I have 

 used eggs of other forms as well — though they show varia- 

 tions, nevertheless point to one conclusion: the period of 

 ectoplasmic changes following fertilization is one of pro- 

 found physical alteration. The changes that I have dis- 

 cussed here which follow the attachment of the sperm-head 

 to the egg-surface sweep over the egg as a wave of explosions 

 that break down material in the ectoplasm. During this 

 period of visible alteration of the egg-surface occur other 

 measurable physico-chemical changes, as oxygen-consump- 

 tion and heat-production. These we may consider briefly. 



The oxygen-consumption by eggs during various stages 

 of development following insemination has been investi- 

 gated by several workers.^ Shearer'- has reported his find- 



^ Warburg, Loeb and Wasteneys, Meyerhof, Shearer. 

 ^ Shearer, ig22. 



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