Lecture XIV. 109 



of the two inner membranes the eight masses the ova are cast 

 out of the oogonium into the cavity of the conceptacle, still loosely 

 held together by the innermost membrane. 



Meanwhile the development of the antheridia is. proceeding. 

 As in the case of the oogonium, the terminal cell becomes the 

 gametangium or sac containing the gametes. In this case, how- 

 ever, its protoplasm breaks up into sixty-four nucleated particles, 

 each of which is very minute and pear shaped, furnished with two 

 cilia, an eye-spot and a yellow chromatophore. These are the 

 sperms. They are launched into the conceptacle, still enclosed 

 in an inner membrane, by the rupture of the antheridium. 

 While the development of the sperms has been proceeding the 

 stalk cell of the antheridial hair produces another cell which 

 displaces the first antheridium and continues the growth of the 

 hair ; branches are formed and numerous antheridia similar to the 

 first are produced as terminal cells. We find therefore that each 

 antheridial hair gives rise to a large number of antheridia in a 

 prolonged succession. The branched hair with its numerous 

 antheridia looks like a minute bush. 



When the tide leaves a plant of Fucus the water imbibed in the 

 frond evaporates slowly and causes a contraction. This seems to 

 squeeze out the detached ova and sperms still enclosed in the 

 inner membranes of the gametangia along with a drop of watery 

 mucilage from the conceptacles. The drop is retained at the 

 opening of the conceptacle by the bunch of hairs issuing through it. 

 Here the inner membranes of the gametangia dissolve or rupture 

 and the gametes are at last entirely free. 



The very minute sperms appear actively motile and swarm 

 round the large ova. One of them embeds itself in the surface 

 of the latter and is gradually absorbed. After it has been thus 

 engulfed its nucleus has been seen to pass across the cytoplasm 

 of the ovum and make its way to the centrally placed nucleus of 

 the latter. A fusion of the two nuclei then takes place. When 

 fertilisation has thus been effected, the ovum loses its attraction 

 for other sperms, and those which previously were aggregated 

 round it move off to unfertilised ova. The oosperm formed 

 in fertilisation immediately secrets a cell-wall over its surface. It 

 'is washed away from the conceptacle-hairs by the returning tide, 

 settles on some solid object and immediately grows into a new 

 Fucus plant. 



No asexual reproductive cells have been found in Fucus. The 

 great morphological and structural differentiation of the somatic 

 cells of Fucus has its counterpart in the complete differentiation 



