PAR THENOGENESIS 



the sea-water which they possessed In their untreated condi- 

 tion, instead they establish it at a new and different level. 



In hypotonic sea-water eggs take up water and increase 

 in volume. If the degree of dilution is effective, the rapid 

 intake of water induces break-down of the eggs' surface- 

 cytoplasm and rapid distension of their vitelline membranes. 

 Removed to normal sea-water they quickly diminish in vol- 

 ume but do not regain their previous state because of the 

 complete break-down at the surface, i.e., complete ecto- 

 plasmic changes. They come again into equilibrium with 

 the surrounding sea-water, but this, owing to the altered 

 surface-structure, is at a new level. 



After having been properly exposed to effective acids in 

 optimum concentration in sea-water, eggs on return to 

 normal sea-water separate their vitelline membranes. That 

 is, the acid treatment induces a change which brings about 

 the subsequent break-down in the surface-cytoplasm. 

 With the processes of restitution by which a new surface- 

 layer forms, the eggs come into a new equilibrium with the 

 sea-water. 



Warm sea-water when effective causes Immediate break- 

 down in the surface-layer. Puncture of the frog's eggs pre- 

 sumably leads also to ectoplasmic break-down. Radiation, 

 as of ultra-violet, brings about ectoplasmic break-down. 

 In these cases as in the others given above, the surface- 

 structure is altered and thus the equilibrium between egg 

 and sea-water is different from that which existed before 

 the treatment. 



Also after fertilization an egg having undergone complete 

 ectoplasmic changes does not return to the state which It 

 had before fertilization with respect to its equilibrium with 

 the sea-water. It shows instead a marked difference. 

 With Its altered surface-layer, the fertilized egg establishes 

 a new equilibrium with the sea-water. As we shall see In 

 the chapter that follows, fertilized eggs exhibit in their 



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