ACTION OF THE SPERMATOZOON UPON THE EGG PVA 
contact with the surface of the protoplasm before entering 
varies in different cases. If the time is long enough the mem- 
brane-forming substance may be given off to the egg and the 
membrane formed, before the spermatozoon has entered com- 
pletely. The formation of the membrane throws the sperma- 
tozoon out of the egg and prevents its entrance permanently, 
since no spermatozoon can penetrate the fertilization mem-- 
brane. Such eggs behave as if they had only undergone mem- 
brane formation by butyric acid. They begin to develop but ~ 
soon perish. If, however, the spermatozoon penetrates through 
the surface of the protoplasm before the membrane-forming 
substance has had time to act the egg can develop. In this 
case, in addition to the membrane-forming substance, the 
corrective substance has penetrated into the egg. 
This idea was supported by the following observation. 
Eggs of a purpuratus were treated with living Asterias sperm in 
hyperalkaline sea-water, and ail formed membranes. Some of 
the eggs were left in normal sea-water as a control; the majority, | 
however, were placed after an hour in hypertonic sea-water ~ 
(50 c.c. sea-water+8 c.c. 23 m NaCl) and at different intervals - 
transferred to normal sea-water. Of the control eggs, about a 
third developed into larvae, while the remaining two-thirds 
behaved like eggs treated only with butyric acid; they began 
to develop and then disintegrated. On the other hand, the - 
eggs which had been exposed for about 30 to 40 minutes to- 
hypertonic sea-water all developed into normal larvae. Dead 
Asterias sperm was absolutely ineffective. This proves, it 
seems to me, in the most striking manner that the spermatozoon 
also induces the development of the egg through two agencies, 
viz., a membrane-forming substance, a ‘‘lysin’”’ and a second 
agent, which has the same effect as the hypertonic salt solution 
in our method of artificial parthenogenesis. It is only when 
both factors contained in the spermatozoon get into the egg 
that the sea-urchin egg develops into a larva. I am unable to 
