Osmunda claytoniana, L. } and O. cinnamomea , L. 59 
later than in O. claytoniana , and continued to form as long as 
the prothallia were kept. While they are always present in 
the large archegonium-bearing prothallia, numerous prothallia 
bearing antheridia exclusively are formed, as is common among 
the Polypodiaceae. These male prothallia are often irregular 
in form, and in O. claytoniana are frequently filamentous, 
especially when they are much crowded (Figs. 29, 30). Upon 
the latter the antheridia may be either terminal or marginal : 
in the flattened prothallia they are borne either upon the 
margin or lower surface, especially of the wings, being of rare 
occurrence upon the midrib. They are relatively large and 
easily seen with the naked eye as little glistening specks 
studding the surface of the prothallia. They arise mainly in 
acropetal order, but new ones may also arise among the older 
ones. In their development the two species agree closely. 
The antheridia are sufficiently transparent to study most of 
the points in the living state, but it was found desirable to 
section them in studying the details of the division of the 
central cell, and the development of the spermatozoids. 
Kny 1 and Sadebeck 2 have described the structure of the 
antheridium in O. regalis , but not very much in detail, and 
Sadebeck's statement that the only difference between the 
Osmundaceae and Polypodiaceae is, that the two ring-shaped 
cells in the latter are in the former divided into two cells 
each, is not borne out, either by Kny’s account or my own 
investigations. 
In studying the divisions in the living antheridium, those 
antheridia should be selected that are on the margin. A cell 
projects slightly above the level of its neighbours, and in it is 
formed a wall cutting off the projecting part. This is quickly 
followed by a second wall that divides the smaller cell into 
two ; an outer cell (Fig. 34 n), nearly triangular in outline, 
and an inner four-sided cell (m). In the former a varying 
number of divisions occur, cutting off from its inner faces 
a series of more or less tabular cells, very much as is the case 
in the segmentation of an ordinary three-sided apical cell. 
1 L. c. p. 9. 2 Sadebeck, in Schenk’s Handbuch, Vol. I. p. 182. 
