Osmunda clayioniana , Z., and O. cinnamomea , Z. 61 
time that the spermatozoids begin to form, they become much 
thicker and very conspicuous, probably at this time undergoing 
a chemical change by which a portion of the cellulose becomes 
converted into mucilage which swells up on the application of 
water. In microtome-sections, stained with alcoholic Bis- 
marck brown, these walls then stain very strongly (Fig. 59), 
while in the earlier stages this is not the case. 
When ripe, or nearly so, the application of water causes the 
antheridium to open, the mechanism being the same as in 
other Archegoniatae. The sperm-cells become isolated, and on 
the rupture of the wall of the antheridium are forced out The 
opening is effected by the forcing off of the opercular cell 
(0), and through the opening thus formed the sperm- cells are 
discharged. Osmunda thus differs from the Polypodiaceae in 
this respect and approaches the Marattiaceae and Bryophytes. 
If the antheridium is perfectly ripe, the walls of the ejected 
sperm-cells are almost immediately dissolved and the enclosed 
spermatozoids liberated ; but the antheridium will often open 
before it is ripe, and in such cases the spermatozoids do not 
escape at once, or if too immature, they may not be set free 
at all. 
Both species proved to be admirably adapted to the study 
of the development of the spermatozoids, and this point was 
critically studied. For the earlier stages of the sperm-cells 
and the changes in the nucleus prior to the formation of the 
spermatozoids, material fixed with a one per cent, aqueous 
solution of chromic acid was employed, and after washing 
and staining with alum-cochineal ; this was sectioned with a 
Minot-microtome. 
If the sperm-cells are examined before the final divisions 
have taken place, the nucleus is seen to be large, and provided 
with a conspicuous nucleolus (Fig. 47). It stains deeply while 
the cytoplasm remains almost perfectly colourless. In the 
later stages the nucleolus becomes less conspicuous ; and after 
the final division, preliminary to the formation of the sperma- 
tozoids, can no longer be certainly seen. 
Nothing noteworthy was observed in the division of the 
