105 





D E 



Fig. 9. — The sperm-sacs and egg-pits of the prothallus of the ferns 

 highly magnified, a'. Surface view of a ripe open sperm-sac. 

 A. Section through it, showing the flattened cells forming its walls 

 and the contained corkscrew-like " sperms." B. The minute 

 wriggling sperms (Sp.) escaping from the sperm-sac into the water 

 adhering to the surface of the prothallus. c. A single sperm still 

 more magnified, d'. Surface view of an open egg-pit. D. Section 

 through an unfertilised egg-pit. Sp. A sperm swimming towards 

 the open mouth of the egg-pit. Con. Cells forming conducting, 

 plug along which the sperm will travel. Ov. Ovule or egg-cell. 

 E. Fertilised egg-pit. In. The orifice. Ov. The ovule now ferti- 

 lised and enlargin^^. 



