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.e. 
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,”’ Pfliiger’s Archiv, CIV, 325, 1904. 
PAS 
