53 
the close relationship existing between the simple cell, and the 
higher and more complex forms belonging to the cryptogamia, if I 
give a brief description of the reproduction of a fern. It is 
hardly necessary for me to allude to the well known brown patches 
on the back of the fronds ; everybody knows that they are spore 
cases and spores, and that from these spores ferns are produced. 
They are not, however, the immediate progenitors of the fern ; 
when the spore falls on a suitable surface, it begins to grow. The 
first indication of vitality is a slight enlargement, and presently 
one or more root-like processes are thrown out from the internal 
cell wall ; these absorb moisture, and the opposite wall of the cell 
enlarges, self-division takes place, ami a new cell is formed, which 
again divides, and an organism is produced scarcely to be distin- 
guished from a marchantia — this is termed the prothallium. A 
further developni ait now takes place — two processes are pro- 
duced, (the analogues of the reproductive organs in flowers,) 
termed antheridia and archegonia — one of the cells of the pro- 
thallium gradually enlarges, and protrudes ; this is at first filled 
with the green colouring matter ; in a short time a small free cell 
is formed within, containing granules and a mucilaginous material 
— these are again developed into fresh cells — it at last separates 
from the prothallium, and becomes an independent organ. The 
cells now increase in size, and contain, when perfectly developed, 
a single spiral filament, with six vibratile cilia ; these escape from 
the cell, and rapidly rotate, thus resembling zoospores in their 
apparent animality — they are technically known as antherozoids : 
the mother cell is termed the antheridial cell. The second pro- 
cess, called the archegonium, is produced by the swelling out of a 
portion of the external layer of the prothallium. At the base is 
an enlarged cell, containing the germ cell ; at the top of the 
archegonium, when fully developed, is a small aperture, through 
which the antherozoids penetrate, and fecundate the germ contained 
in the germ cell, which rapidly becomes the primordial cell of the 
new plant ; cells begin to form and subdivide, and gradually 
diflerentiate into special organs as roots, stems, and leaves. 
I would now call your attention to the resemblance, on the one 
hand, to the reproduction of the simple vegetable cell, by a ciliated 
motile spore, and on the other, to the flowering plants ; we may 
compare the prothallium to the flower — the antheridine cell to a 
