PTERIDOPHYTA. 



'39 



when the neck-canal contained many spermatozoids, and when one lay 

 against the receptive spot, but had not penetrated. 



On entering the extruded mucilaginous substance the spermatozoids 

 leave their vesicles behind, and their motion is retarded. The cork- 

 screw spiral is drawn out and the number of turns apparently increased. 

 The forward motion of the spermatozoid is accompanied by a rotation 

 which corresponds to the pitch of the screw. 



The behavior of the spermatozoid after entering the egg can be fol- 

 lowed only in properly fixed and carefully stained sections. Shaw 

 found that in all prothallia killed within an hour after the entrance of 

 the spermatozoid into the archegonium the egg-cells were in a collapsed 

 condition, being concave on the outside, and the nucleus conforming 

 to the shape of the cell (Fig. 55, A). The concavity of the egg-cell 

 occupies the position of the receptive spot. This condition was 

 regarded by Shaw as normal, and not the result of killing reagents, 

 since in the living condition spermatozoids were seen moving freely in 

 the cavity above the egg. I quote as follows : 



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, O. struthiopteris 

 (Campbell, '95)) as having a large hyaline receptive spot. 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 sper- 

 matozoids 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 could 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 sper- 

 matozoid 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 

 the egg from injury or from multiple fertilization by them. 



In sections made from material killed in both chrom-acetic and 

 chrom-osmic-acetic acid the author has also observed in many cases 

 the collapsed condition of the egg-cell as described by Shaw. Several 

 preparations were, however, especially interesting as they tend to throw 

 some doubt upon the collapsed condition being a normal occurrence. 

 In one of these two or more spermatozoids had entered the egg, one of 

 which, or rather its nucleus, had partly penetrated the egg-nucleus; 



