Shaw . — The Fertilization of Onoclea. 275 
All the sections of prothallia that were killed within an 
hour after the entrance of the spermatozoids into the arche- 
gonia, show the eggs in a collapsed condition (Figs. 1 and 2), 
concave on the outer side, and the nucleus in each conforms 
to the shape of the cytoplasm. In this state the shape of the 
egg is about the same as it is in the unopened archegonium 
after the canal-cells have swelled. The return to this form 
may have been due to the action of the fixing or imbedding 
agents, the egg in this stage being more susceptible to their 
shrinking influence, either because it is not at this time in the 
state of tension which it acquires later, or because the open 
canal permits the rapid access of the plasmolizing agents. 
There are reasons to believe, however, that the collapse is not 
an artificial plasmolysis, but that it takes place as soon as the 
spermatozoid enters the egg. The mature egg has been 
described (for the other species) as having a large hyaline 
receptive spot 1 . The concavity of the collapsed egg occupies 
the position of that spot. That it was formed before the 
plants were killed seems evident from the movement of a 
number of spermatozoids in the venter. This can be seen 
in the living plants. That the number of these spermatozoids 
is large is shown by the specimens stained and sectioned. 
They can hardly have been carried into the venter by the 
fixing agent, for those in the canal were fixed first, in the 
extended condition, and those in the venter afterward, in 
the contracted form. From the evidence at hand it appears 
that as soon as the egg is entered by a spermatozoid it loses 
its turgidity, and the spermatozoids which come into the 
venter afterward meet with little or no resistance from the egg. 
It may be that the turgid condition of the egg, in the first 
place, offers mechanical facility for the screw-like sperma- 
tozoid coming through the narrow base of the neck to force 
itself into the cytoplasm of the receptive spot ; and that 
the plasmolytic condition of the egg afterward deprives the 
following spermatozoids of this advantage, and protects 
Campbell ’95, Fig. 159. 
