172 
STRUCTURE AND LIFE HISTORIES 
extruded from the archegonia contains a substance (malic 
acid, in some ferns) which stimulates the sperms to swim 
toward it. This they are enabled to do by the free 
external water. On reaching the archegonia, they enter 
it, and swim down the neck-canal to the egg. The sperm 
that first reaches the egg penetrates it, and passes through 
FIG. 130. Fertilization in the fern, Onoclea. A, longitudinal section 
of archegonium, showing the egg in the venter, and numerous sperms 
passing down the neck-canal. B, an egg-cell in the venter. One sperm 
has entered the nucleus, three sperms have failed to enter the egg. (After 
W. R. Shaw.) 
its cytoplasm until it reaches the egg-nucleus, with which 
it fuses, thus completing the act of fertilization (Fig. 130). 
As soon as one sperm enters the egg-cell, the latter at once 
forms a. fertilization-membrane about itself, through which 
the remaining sperms cannot enter. 
167. Nature of the Fertilized Egg. It will at once be 
recognized that the fertilized egg, resulting from a union 
