Thorn — Fertilization in Aspidium and Adiantum. 297 



of sections of egg-cells. The opening v is then only the 

 cross-section of the cavity which the ventral canal-cell occu- 

 pied at an earlier stage as figure 43. In figure 44a the edge of 

 the cavity is indicated by the dotted curved line as lying below 

 the plane of the section ; in 44b and 44c, which are succeeding 

 sections of the same egg, it becomes very prominent. If the 

 cell were followed through, the same appearance as 44a 

 would be reached on the other side, or if a median section 

 perpendicular to the plane of 44c were taken the figure would 

 be nearly the same as 44c. Such openings surrounded 

 by egg-cytoplasm can easily be mistaken for a " recep- 

 tive spot " developed in the egg itself when they are 

 really outside the cell. This concavity is not uniform 

 in its development, nor when present does it always show 

 as in the diagrams. It lies at the bottom of the neck 

 of the archegonium. The position of the neck of the 

 archegonium varies from almost perpendicular to the 

 surface of the prothallium (fig. 2) when the ventral canal 

 cell lies near the center of the egg, to an angle of less than 

 forty-five degrees (figs. 1, 9 and 43) when the cavity usually 

 lies far to one side. The egg-cell adapts its form to the 

 shape of the cavity in which it lies. This concavity in its 

 surface is not always present. In the egg shown in figures 

 6, 7 and 8 there was no such spot in any section. Instead 

 we find a decided convexity of surface while the spermat- 

 ozoid (s) is seen entering the cytoplasm a little to one side of 

 its pointed end. This seems to be but another evidence of 

 the amoeboid character of the e^sr. Shaw describes such 

 figures as this, as a change from a concave surface to a con- 

 vex surface occurring in the living cell as soon as the pressure 

 of the ventral canal-cell is removed. He suagests that it is 

 a readjustment due to turgidity of the egg and states that it 

 returns to its former shape as soon as the spermatozoid has 

 entered. Such a change from a concave surface to a convex 

 surface probably did occur in the egg shown in figure 6, but 

 it cannot be a constant phenomenon, for I have observed it 

 only once or twice in the large number of archegonia exam- 

 ined. Further I see no evidence of any return to the former 

 shape either in figure 6 or in any other sections examined. 



