THE ALG.E 



239 



'Eggs 



in the separation of the mother cells of the future gametes by 

 membranous walls. In this internal cell division a cleavage of the 

 cytoplasm around each nucleus is followed by the simultaneous 

 secretion of the membranous walls between the mother cells. 

 The protoplast of each mother cell then rounds up in the female 

 gametangium (Fig. 128, b and c), the dividing membranous walls 

 are absorbed, and the gametes 

 are ready to be expelled from 

 the gametangium. In the male 

 gametangium (Fig. 129) simi- 

 lar processes occur, except that 

 the male gametes differentiate 

 to form two laterally attached 

 cilia and a brick-red eyespot in 

 a more or less pear-shaped male 

 gamete. When the gametes are 

 fully formed, they are expelled 

 into the sea water through 

 the pore of each reproductive 

 cavity embedded in a slimy 

 substance. This expulsion of 

 gametes usually occurs at low 

 tide, when the reproductive 

 branches dry and contract in 

 the sun, thus squeezing out 

 the contents of the reproduc- 

 tive cavities. When first ex- 

 pelled, the male and female gametes are both inclosed in the 

 inner membranous layer of the gametangium wall, but this soon 

 ruptures and the individual gametes become free-floating cells 

 (Figs. 128, d, and 129, 5). With the return of the tide the 

 gametes from the male plants are mixed freely with the female 

 gametes in the sea water, and abundant fertilizations occur, as 

 is evidenced by the great number of these plants in locations 

 favorable to their existence. 



In the process of fertilization the female gametes float 

 impassively in the water, but the male gametes swarm in great 



FIG. 128. Development of the oogonium 

 and eggs in Fucus 



a, young oogonial cell with eight free 

 nuclei; &, older oogonium divided to 

 form eight eggs ; c, eggs in the oogonium 

 rounded up preparatory to expulsion as 

 in d. After Thuret 



