98 
PROFESSOR A. ANSTRUTEER LAWSON ON 
than that shown in fig. 7. The wall cells have increased in number, and the inner 
cells have undergone mitosis, their delicate cell walls separating the nuclei. There 
are eight inner ceils shown in the section. As this is a median section, it represents 
the sixteen-cell stage of the inner antheridium. The dense granular cytoplasm and 
the large deeply staining nuclei render these cells sharply differentiated from the 
vegetative cells. The young antheridia in section appear at this time as conspicuous 
semicircular protuberances projecting from the surface of the prothallus. 
A still older stage in the development of the antheridium is represented in fig. 9. 
Here it will be seen that the inner cells have undergone repeated mitosis. There 
is now a large central mass of sperm-mother cells, or spermatocytes. The wall cells 
have also enlarged, and the young antheridium as a whole has increased to more than 
twice the size of that shown in fig. 8. 
A more mature stage is represented in fig. 10. At this time the antheridium 
has become almost spherical in form and increased greatly in size. The number of 
spermatocytes is apparently the same as that in stage shown in fig. 9, but the 
internal space has increased greatly, and the spermatocytes are less crowded. These 
latter seem now to be separating from one another by intercellular spaces. In 
fig. 11 we have represented a tangential section of a nearly mature antheridium. The 
nuclei of the spermatocytes have undergone a change. They appear now as very 
dense crescent-shaped or coiled bodies, that stain deeply. These are the immature 
spermatozoids. In one or two instances these spermatozoids seemed to be ciliated, 
but the nature of the cilia was not made out with certainty. They seemed to be of 
the same nature as those of Psilotum, which will be described in detail in the follow- 
ing pages. An external view of a mature antheridium showing only the wall cells, 
is represented in fig. 12. 
The Archegonia. 
As stated above, there is clearly no differentiation of a vegetative and reproductive 
region of the prothallus. It would seem that any part of the surface of the prothallus 
may give rise to archegonia as well as antheridia. In all cases examined the 
archegonia w~ere much more numerous than the antheridia. In the young prothalli 
one will probably find very few archegonia ; but as the development proceeds they 
become very numerous and widely distributed over the surface. I have counted as 
many as fifty archegonia in one field of the microscope. A fair sample of the 
manner of their occurrence is "indicated in fig. 2, which represents the end of a 
branch of the prothallus. From the view there shown one may look down into the 
necks of ten archegonia. If this specimen were turned over there would be quite 
as many archegonia found on the opposite side. This figure also shows the small 
size of the archegonia as compared with the antheridia. Looking down from the 
surface view it is quite clear that the neck of the archegonium consists of four rows 
of cells ; and these project beyond the surface — the venter remaining below the 
