64 Campbell . — On the Prothallium and Embryo of 
antheridium, the wall is still very evident, but soon is com- 
pletely dissolved and the spermatozoid escapes. The latter 
resembles more nearly the spermatozoid of Equisetum than 
that of the other ferns. There are but two complete coils, 
usually, and the hinder one is relatively larger than in the 
Polypodiaceae (compare PI. V, Figs. 57, 58). In swimming 
there is a peculiar undulating movement of the large hinder 
coil that recalls strongly the movement seen in the sperma- 
tozoids of Equisetum . Attached to the hinder coil, and often 
adherent to it, is the usual vesicle, the remains of the central 
part of the sperm-cell. It quickly takes up water and 
becomes much enlarged, and when the spermatozoid is killed 
with iodine in iodide of potassium, it swells up to several times 
its original size. This reagent also swells the body of the 
spermatozoid. To study the free spermatozoids most satis- 
factorily, osmic acid is the best fixing agent. A drop of the 
dilute acid, followed by a drop of weak alcoholic methyl-violet, 
stains both the body of the spermatozoid and the cilia, and is 
especially useful in the study of the latter. They are attached, 
not directly to the pointed end, but to the coil below, and 
cover considerably more space than described by Buchtien \ 
who limits them to a very narrow area. 
The final divisions of the sperm-cells are simultaneous, so 
that the spermatozoids all mature about the same time. 
Their number is large, usually 100 or more. 
On comparing the structure of the antheridium and sperma- 
tozoids with those of other Pteridophytes, we find that in the 
form of the antheridium and the arrangement of the peripheral 
cells, the Hymenophyllaceae 2 and Gleicheniaceae 3 are the 
nearest among the ferns to the Osmundaceae, and that the 
Gleicheniaceae seem to stand between them and the Poly- 
podiaceae. There are, however, points of resemblance to the 
Equisetaceae, in the earlier divisions of the antheridium, and 
its large size, and to the Marattiaceae in the arrangement of 
1 Buchtien, Entwickelungsgeschichte des Prothallium von Equisetum, p. 38. 
2 Bower, The Oophyte of Trichomanes ; Annals of Botany, Vol. I. 
3 Rauwenhoff, 1. c. p. 42. 
