Osmunda clay Ionian a, Z., and O. cinnamomea , Z. 67 
a young archegonium of 0 . cinnamomea in which the nucleus 
of the outer cell is in process of division, while that of the still 
undivided inner cell is just preparing for division. 
By the time the young archegonium has reached this three- 
celled stage, it is easily recognized, but still very small, and 
the contents of the cells differ somewhat from that of the 
adjacent cells. The nuclei are larger and the protoplasm, 
especially of the middle cell, denser. Of the three cells 
usually present, the outer is the mother-cell of the neck, the 
second the mother-cell of the egg and canal-cells, and the 
lower simply divides once or twice, and contributes to the 
formation of the venter of the archegonium. 
The neck- mother-cell divides by a vertical wall into equal 
parts which are almost immediately divided again by others 
at right angles to the first, and these four cells, as usual, give 
rise to four rows of neck-cells (see Figs. 63, 64 h). Before 
any further divisions occur, the neck-cells begin to project 
above the surface of the prothallium, and the central cell 
enlarges and its upper wall becomes strongly convex (Fig. 64). 
The primary neck-cells now elongate rapidly, and divide re- 
peatedly by transverse walls, until the neck consists of four 
rows of from 5 to 7 cells each (Figs. 66, 67). Some further 
elongation takes place after the divisions are completed, but 
this is due in part to mere mechanical stretching caused by 
the absorption of water. As the neck elongates, the upper 
part of the central cell grows up with it and is soon separated 
by a wall from the lower part (Plate V, Fig. 65 c). This is 
the primary canal-cell, and soon after a second cell, the ventral 
canal-cell, is also separated from the central cell (Fig. 66). It 
has been generally supposed that the ventral canal-cell is the 
equivalent of one of the polar bodies in the animal ovum, and 
that it is cut off shortly before the egg matures ; but in both 
species of Osmunda examined by me, it is formed long before 
the archegonium is ripe. After the separation of the ventral 
canal-cell, a further division of the primary canal-cell occurs. 
Usually this seems to be confined to the nucleus, but in O. cin- 
namomea (Fig. 69) two cases were seen where a very evident 
