480 Davis . — The Origin of fhe Archegoninm . 
each of which develops a sperm. The antheridium is then 
a capsule of sterile tissue enclosing a mass of fertile cells. 
The archegonium presents peculiarities of form and certain 
structural features that obscure its fundamental agreement in 
structure with the antheridium, but a close study of its develop- 
ment makes the homology of these organs clear. The arche- 
gonium, like the antheridium, arises from a single superficial 
cell, which divides in such a manner that a growing point is 
generally established, sometimes with a single apical cell, 
sometimes terminated by a group. This growing point, acting 
as a whole, builds up the archegonium, which is thus a unit 
from its earliest inception. At maturity the archegonium is 
a long narrow capsule, whose outer layer of cells encloses 
a central group. This central mass is a line of cells, some- 
times numerous, running the entire length of the structure. 
Of these only the lower cell develops a gamete, its contents 
rounding off as an egg. The other cells (canal-cells) break 
down. 
Generally the cells of the central mass form a single row, 
but Mr. G. M. Holferty has recently found among the Mosses 
that there may be two or more rows of canal-cells at various 
levels of the archegonium, but especially near the tip. His 
results have not yet been published, but their bearings on the 
present problem are so important that I have asked the privi- 
lege of announcing them in advance. Such conditions are 
identical with certain stages in the development of the an- 
theridium, and establish clearly the homologies between these 
sexual organs. It seems almost certain that the canal-cells 
at one time produced gametes, and are therefore homologous 
with one another and also with the cell that develops the egg. 
The entire group, canal-cells and the egg, is homologous with 
the mass of sperm-producing tissue of the antheridium. 
The archegonium is therefore a gametangium which has 
passed through an evolution characterized by such extensive 
sterilization of the reproductive cells that finally only one 
gamete is formed in the structure. The sterilization was 
progressive from the terminal region backwards, so that 
