3i8 



SENESCENCE AND REJUVENESCENCE 



In the mosses and ferns the separate history of the germ cells 

 may in the male extend back to an early stage in the development 

 of the male sexual organ, the antheridium, where the sperma- 

 togenous cell or cells become separated from the cells of the 

 antheridial wall. Fig. 132 shows the stage of development of the 

 antheridium in which the spermatogenous cells first become segre- 

 gated in Riccia, one of the liverworts. After their segregation 



Figs. 128-131. — Gametes of fungi: Fig. 128, oogonium of SaproUgnia, contain- 

 ing several eggs and antheridial tube piercing its wall in fertilization (from Coulter, 

 etc., '10); Figs. 129-131, three stages in formation and union of gametes in Mucor 

 (from Brefeld, '72). 



the spermatogenous cells undergo numerous divisions and finally 

 give rise to spermatozoids. 



The female gamete, on the other hand, is not separated from 

 other non-gametic cells until the last division preceding fertihzation. 

 Figs. 133-39 show the development of the archegonium of Riccia. 

 The divisions of the central cell in Fig. 135 produce the four neck 

 canal cells and the ventral cell (Fig. 137). Fig. 138 shows the 

 division of the ventral cell which gives rise to the ventral canal 



