30 THE LIFE-HISTORY: OF A FERN 
medium of transit of the spermatozoids to the ovum. But the movements 
of the spermatozoids are not subject to blind chance: the chemiotactic 
attraction of the archegonium directs the spermatozoids through the water, 
towards the open neck, which they may be seen to enter, and finally one 
of the spermatozoids coalesces with the ovum: fertilisation is effected 
Fic. 14. 
Young embryo of Adiantum concinuum. L=\eaf-quadiant; S=stem-quadrant ; 
R=root-quadrant ; #=foot-quadrant. (After Atkinson.) 
by the absorption of the male nucleus in that of the egg (Figs. 13 
and 13 dis). Thus the presence of external fluid water 1s essential for the 
process of fertilisation. without it the prothallus 7s unable to achieve that 
object of tts existence. 
The consequence of fertilisation is the growth and segmentation of 
the ovum, or zygote, as it may now be called, to form a mass of 
embryonic tissue, which at first remains embedded in the tissue of the 
