70 Campbell . — ( 9 ^ the Prothallium and Embryo of 
Fertilization. 
The entrance of the spermatozoids may be readily seen, 
but owing to the number of cells surrounding the venter of 
the archegonium, it is difficult to see the penetration into the 
egg in the living archegonium. This is more easily seen in 
O. claytoniana than O. cinnamomea. To see the process, 
a number of male prothallia that had been kept rather dry 
for a few days, were teased out in a drop of water, and after 
lying in this for a few minutes, or until a sufficient number of 
spermatozoids had escaped, were transferred to a slide, upon 
which a female prothallium with ripe archegonia was placed 
with the lower surface uppermost, and covered with water. 
The horizontal position of the archegonia makes it easier to 
note the entrance of the spermatozoids, and to follow them 
down to the egg, than is the case in most ferns ; but as before 
stated, it is not possible to follow certainly the further history 
of the spermatozoid in this way. 
Within a few minutes the ripe archegonia open, and the 
spermatozoids, attracted by the substance discharged from 
the archegonium, collect about its open mouth, and very soon 
one finds its way in. With the ciliated end down it revolves 
rapidly, not seeming to be much impeded in its movements by 
the mucilaginous matter thrown out by the archegonium, as is 
usually the case. Suddenly, with a quick movement, unlike 
the slow, worm-like movement observed in most ferns, it slips 
through the neck down to the central cell, where its rotary 
movement is resumed. After about three or four minutes it 
can no longer be seen, and presumably is within that time 
taken up by the egg. Other spermatozoids usually make 
their way into the central cell, but so far as observed only one 
ever penetrates the egg. After fertilization is effected, the 
lower neck-cells approach, but not enough to prevent the 
passage of other spermatozoids. Within a few hours the inner 
walls of the upper neck-cells begin to show the brown colour 
always seen in the fertilized archegonium. 
To study the changes that take place after the entrance of 
