490 Davis . — The Origin of the Archegonium. 
degenerate gamete mother-cells can hardly be stronger, apart 
from the actual existence of such a series of organs as we have 
postulated. 
To complete the agreement between such structures and 
the archegonium and antheridium we have only to understand 
the manner in which the terminal openings of these organs 
would be differentiated. These points of exit and entrance 
are conveniently situated, but there are probably more im- 
portant reasons for their selection. The apex of the pluri- 
locular sporangium is the situation where the gametes first 
mature and from which they first escape. And this would 
probably lead to the choice of such a point of dehiscence 
if the archegonium and antheridium were derived from this 
structure. 
We have, naturally, very little direct evidence bearing on 
such evolutionary processes as we have just discussed. But 
the writer can see nothing in the structure, development, or 
behaviour of the archegonium, antheridium, or plurilocular 
sporangium that offers serious objections to the hypothesis 
presented. The difficulties are in the absence of intermediate 
stages, which cannot of course be presented unless forms exist 
that illustrate these conditions. The value of the hypothesis lies 
largely in its suggestiveness for further research, but it seems 
to the writer to offer an explanation far more acceptable than 
other views. Attempts to relate the archegonium to the 
oocysts of heterogamous Algae do violence to the fundamental 
character of their organization, as was shown at the beginning 
of the paper. This hypothesis, which carries the origin of 
the archegonium much farther back in point of time, seems 
safe in its reasoning and thoroughly consistent with the evo- 
lutionary principles of sex and tissue-differentiation. 
To make the chief points in this paper clearer, and also as 
a summary, we have constructed diagrams (Fig. 21) illustrating 
other and each with a ventral canal-cell. It was evident that the upper egg had 
developed from the lowest canal-cell. Such abnormalities are to be expected, 
according to our theory of the archegonium. Mr. Holferty has observed similar 
examples. 
