THALLOPHYTES 



43 



posed of eight triangular, platelike cells known as shields (fig. 115). 

 Projecting centripetally from the center of each shield is an elongated 

 cell (manubrium), which bears a terminal cell (head cell). These head 

 cells give rise to a varying number of similar cells, and each ultimate 

 cell produces a pair of long filaments, each consisting of approximately 

 200 cells, each cell producing a single sperm (figs. 117, 118). The in- 

 terior of the antheridium, therefore, is a tangle of filaments, and the 



115 



FIGS. 115-119. CJtara: 115, branch bearing 6ogonium (showing its sterile jacket 

 and crown) and antheridium (showing its interlocking, shieldlike wall cells); 116, young 

 oogonium (stalked and not yet completely invested by the jacket) and antheridium; 

 117, manubrium bearing head cells and sperm-containing filaments; 118, detail of cells 

 of filament showing contained sperms; 119, sperms (spirally coiled and biciliate). 

 After SACHS. 



sperm output of a single antheridium may range between 20,000 and 

 50,000. The sperm is a more specialized structure than is the zoospore- 

 like sperm of the ordinary algae, and more resembles the sperms of 

 higher plants. The nucleus with its sheath of cytoplasm forms the body ; 

 the cytoplasm extends to form an elongated more or less spirally coiled 

 beak, and from its tip two long cilia are produced (fig. 119). 



Oogonium. The oogonium, which replaces a secondary branch, is 

 an enlarged apical cell, and produces a single large egg filled with starch 



