424 Wilson . — Spermatogenesis in the Bryophyta , 
difficulty was experienced in determining the relative ages of the various 
antheridia in which dividing cells were found ; this was especially the case 
in antheridia which were almost mature. As several investigators have 
pointed out, the whole of the cells in an antheridium do not divide at the 
same time, but division takes place simultaneously in all the cells of 
a definite group. It is probable that a division is completed in the cells of 
all the groups before any group enters upon the succeeding mitosis. As, in 
the great majority of cases, the same number of spermatozoids is produced 
in each antheridium, it follows that at any given stage of development the 
number of cells present in different antheridia is approximately constant. 
The number of cells in the later stages is obviously very large, and no 
attempts were made to estimate the total. As will be described later, after 
the final division, the spermatids become rounded, and there is therefore no 
difficulty in distinguishing this stage. The number of spermatids occurring 
across the median longitudinal plane was ascertained, and this was com- 
pared with countings made in a similar manner in younger antheridia. The 
following results were thus obtained : — 1 
Average number of spermatids across antheridium . . . 13-14 
Average number of cells across antheridium immediately before final 
division ........ 10-11 
Average number of cells across antheridium immediately before pen- 
ultimate division ....... 8 
Average number of cells across antheridium immediately before anti- 
penultimate division . . . . . .4-5 
In a few cases, apparently, an additional division had taken place, for 
antheridia, already possessing on the average fourteen cells across the 
median plane, showed groups in which divisions were still proceeding ; but 
these cases were quite exceptional. 
As the multiplication of spermatogenic cells goes on the antheridium 
grows considerably, but this increase in size does not keep pace with cell- 
division. The spermatogenic cells, therefore, become progressively smaller 
as maturity is approached. This fact affords confirmatory evidence as to 
age. Measurements of the cells found in antheridia at different stages of 
development were made, but these did not give constant results, probably 
on account of the variable shape of many of the cells. The distance 
1 By making certain assumptions the number of cells which should be found across the 
antheridium when cut in the median longitudinal plane can be calculated. After each successive 
division the number is increased in the proportion 1 :^/ 2 . If eight cells are found before the 
penultimate division 8 (^2) = 10-08 should be present after its completion and 8 (^2) 2 = 12.7 after 
the close of the final division. How closely these numbers approximate to those obtained by actual 
observations may be seen by a comparison of those given above. I am greatly indebted to Mr. Odell, 
A.R.C.S., for information as to the factor (\/ 2) involved. 
