THE PTERIDOPHYTA : FILICALES, THE FERNS 



497 



formed into a tapering spiral of three turns, with a vesicle of cytoplasm at 

 the posterior end. A dense band, called the blepharoplast, attached to the 

 edge of the spiral at the thin end, bears a group of very long flagella, by means 

 of which the antherozoid can swim actively in the water film between the 

 prothallus and the soil. When the antherozoids are mature the walls of 

 the mother cells become mucilaginous and swell, forcing off the lid cell 



^%\;\\ 



Fig. 487. — Dryopteris filix-mas. Mature antherozoid with 

 protoplasmic vesicle and flagella. {After Yamauouchi.) 



of the antheridium. The antherozoids are ejected, each still contained in 

 a cell wall, but this quickly dissolves and liberates the male gamete, which 

 soon sheds all its adherent cytoplasm (Fig. 487). 



The archegonium is an elongated organ, consisting of a venter, which 

 is buried in the tissues of the prothallus, and a curved neck, which projects 

 freely above it. The archegonium originates by the division of a superficial 

 cell into two (Fig. 488). The lower of these is the basal cell, which con- 

 tributes only to the building of the wall round the venter. The upper cell 



