XXII 

 THE ACTION OF THE SPERMATOZOON UPON THE EGG 



I. HETEROGENEOUS HYBRIDIZATION 



1. In 1905 the writer showed that in the sea-urchin egg 

 artificial parthenogenesis is produced by two agencies, one of 

 which causes membrane formation while the second one serves 

 to make the development more normal. In 1906 he expressed 

 the idea that the spermatozoon also caused the development 

 by two different agencies, one of which induced membrane 

 formation while the other one acted as a corrective — ^like the 

 hypertonic solution.' We will now consider the proof for this 

 statement. 



The eggs of the sea-urchin cannot be fertilized by the sperm 

 of the starfish under normal conditions. In 1903 the writer 

 found that the eggs of S. purpuratus can easily be fertilized by 

 the sperm of the starfish if we render the sea-water a little 

 more alkaline. If 0.6 c.c. N/10 NaOH is added to 50 c.c. 

 sea-water and sperm of a starfish (Asterias) is added, all the 

 eggs form a typical fertilization membrane.^ 



After adding the sperm of Asterias to the eggs of S. purpur- 

 atus, it is noticeable that not all the eggs which form membranes 

 develop into larvae. Some of them begin to segment after the 

 usual interval, but others behave like eggs which have only 

 formed membranes under the influence of butyric acid. For at 

 15° C. they begin to proceed toward nuclear division, but then 

 most of them go to pieces within a few hours. I thought at 

 first that in these eggs we were dealing, not with an influence of 

 the spermatozoon, but with the effect of the extraneous body 



1 Loeb, "Versuche ueber den chemischen Charakter des Befruchtungsvor- 

 ganges," Biochem. Zeitschr., I, 183, 1906. 



2 Loeb, "Weitere Versuche ueber heterogene Hybridisation bei Echino- 

 dermen," Pfiager's Archiv, CIV, 325, 1904. 



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