62 Campbell. — On the Prothallium and Embryo of 
nuclei, and owing to their small size it was not possible to 
decide the number of the nuclear segments. At all stages the 
nucleus stained deeply with the alum-cochineal. 
After the final divisions, the nuclei remain slightly flattened 
in the plane of division, recalling somewhat the same stage 
in Pellia 1 . 
After the final division is completed, the nuclei gradually 
assume the form of resting nuclei before the differentiation of 
the spermatozoid begins (Figs. 48, 49). The nuclear segments 
become less distinct, and the chromatin more uniformly dis- 
tributed. About the same time, the walls of the sperm-cells 
begin to acquire their mucilaginous consistence, and readily 
separate. 
The development of the spermatozoids may be readily 
followed, and corresponds essentially to that of the other 
Pteridophytes and Bryophytes. The first sign of the forma- 
tion of the body of the spermatozoid consists in the appearance 
of a cleft or depression on one side of the somewhat flattened 
nucleus (Fig. 50). This increases in depth, the nucleus in the 
meantime contracting, until, seen from the side, it appears 
crescent-shaped, and is really a short, thickish band. The 
two ends of the band now lengthen, the whole becoming 
narrower and thinner, and the nucleus gradually assumes the 
form of a flattened spiral, with one end tapering to a fine point 
and more closely coiled than the other end. The young 
spermatozoid lies perfectly free in the sperm-cell, and is no- 
where in contact with its wall (Figs. 51-53). 
In the full-grown spermatozoid there are about two com- 
plete coils which form a much flatter spiral than is common 
among ferns. This flattening is due to the flattened form of 
the nucleus of the sperm-cell, and recalls the form of the 
spermatozoid in some of the Bryophytes and in Equisetum 
rather than those of the Polypodiaceae, where, even in the 
sperm-cell, the spermatozoid has the elongated cork-screw 
1 Campbell, Zur Entwickelungsgeschichte der Spermatozoiden ; Ber. der 
Dentschen Botanischen Gesellschaft, 1887. 
