178 ADVANCED FORMS OF REPRODUCTION" 



cells of a filament which become greatly enlarged and spherical 

 or ovoid in form (Fig. 116, A, B). The female gamete is motion- 

 less but the colorless region on one side of the gamete certainly 

 suggests the idea that this body is related to the zoospores and 

 male gametes, but that it has lost its cilia. At maturity, open- 

 ings of various kinds appear in the oogonium through which the 

 male gametes enter and one fuses with the female (Fig. 116, A, 



Fig. 116. Sexual reproduction of Ocdogoiiium: A, portion of a filament 

 in which a female gamete has been formed — o, opening in cell wall for 

 entrance of male gamete. B, portion of filament showing formation and 

 escape of male gametes. C, gametospore free from mother cell. The 

 germination of this spore results in the rupture of its outer wall and the 

 protrusion of the contents of the spore as four cells which are for a time 

 retained by the delicate inner wall of the spore, as shown in D. E, the 

 four cells have become mobile zoospore and the delicate inner wall of the 

 spore is greatly distended and about to rupture. F, G, stages in the 

 germination of the zoospore. — After Hirn. 



o). The thick-walled gametospore that results from this union is 

 set free by the decay of the oogonial walls and germinates after 

 a resting period very much as in the case of Ulothrix. The 

 contents of the gametospore is extruded through the ruptured 

 wall as a delicate sac and then divides, forming four zoospores 

 which produce new plants (Fig. 116, C-G). The question will 

 naturally arise as to the force that brings these and other gametes 

 together. The frequently observed aggregation or swarming of 



