S06 * FRANK R. LILLIE 
pearance of the fertilization membrane of echinids might be 
similarly due to excretion of a cortical colloid which is removed 
by diffusion and hence is not detected. It is a problem worthy 
of careful investigation whether the loss of cortical colloids is not 
the first step in fertilization generally. 
II. PARTIAL FERTILIZATION 
Two functions of the spermatozoon in fertilization may be 
sharply distinguished. The first is the initiation of the develop- 
ment and the second is the transfer of paternal qualities to the 
fertilized ovum (heredity from male parent). The first function 
alone is under consideration in these experiments. 
We have seen that in Nereis the immediate effect of attach- 
ment of the spermatozoon is essentially the same as a mechanical 
shock (centrifuging), or a chemical stimulus (KCl); that is, it 
causes the breaking down of the cortical emulsion and consequent 
formation of the gelatinous envelope of the egg. But apparently 
the resemblance extends no farther, for in the case of mechanical 
or chemical stimulation the impulse to development is lost or 
greatly weakened after maturation has occurred; and the eggs 
do not segment. On the other hand the normally fertilized egg 
does not stop after maturation, but proceeds with its develop- 
ment in a normal fashion. Now the cause of this difference 
might be either: (a) because the stimulus of the spermatozoon 
is qualitatively different from, or stronger than, mechanical or 
chemical stimulation, or (b) because the fertilizing action of the 
spermatozoon is not completed with the cortical changes but 
continues after its entrance into the egg. If the first alternative 
were correct, then the elimination of the spermatozoon after 
membrane formation should not prevent the normal cleavage and 
development of ova which had once been stimulated by it; but 
if the second alternative were correct and the sperm nucleus 
were prevented from entering the egg after it had induced mem- 
brane-formation, then such ova should proceed no further in 
their development than those mechanically or chemically stimu- 
lated. 
