104 OUTLINES OF EVOLUTIONARY BIOLOGY 



to those of Fucus, being hollow sacs in which the male gametes 

 are developed. The latter (Fig. 51, s.) are active spermatozoa, 

 each having a spirally coiled body, 

 consisting chiefly of chromatin 

 material, and bearing a bunch of 

 cilia at one end, by the vibration of 

 which the gamete swims actively 

 about in any dew or other moisture 

 which may be deposited on the 

 prothallus. 



The archegonia (Fig. ,52) differ 

 considerably from the oogonia of 

 Fucus, having a characteristic 

 structure which is more or less 

 accurately repeated in the corre- 

 sponding organs of all the higher 

 plants. Each consists of a hollow 

 swollen venter, sunk in the tissue 

 of the prothallus, and a long neck 

 which projects from the surface, 

 and the wall of which is composed 

 of four rows of cells. The venter 

 contains a single relatively large ovum or oosphere (Figs. 52, A, o, 

 and 52, B), above which an axial row of canal cells (A'', K") 



FIG. 51. Antheridiumof aFern, 

 discharging Spermatozoa 

 (Antherozoids) from its 

 opening, highly magnified. 

 (From Vines' " Botany.") 

 a, antheridium ; s, spermatozoon. 



FIG. 52. Archegonia of a Fern, Polypodwm vulyare, X 240. (From 

 Strasburger.) 



A, young, showing ovum(o) and canal cells (K',K"), and with the end of the neck closed 



B, mature, with the end of the neck open. 



extends into the neck. When the ovum is ready for fertilization 

 the canal cells degenerate into mucilage and the cells at the end 



