EMBEYOGENT IN ALG^. 



271 



from the upper part of the membrane of the androspore. This 

 antheridium, at first unicellular, divides into two cells, which become 

 the mother-cells of the spermatozoids. The whole plastic contents of 

 each mother-cell are employed in the formation of a single spermato- 

 zoid of considerable size. When the spermatozoids are mature then 

 the upper spermatozoid raises slightly the lid of the antheridium 

 (fig. 479, 1, 2, c). In the meantime the female organ is going 

 through a pf ocess of development. When its contents are mature, the 

 membrane of the female organ is ruptured all at once a little below 

 its summit, the upper part forming a sort of lid, and the filaments 

 which surmount it are turned to the side by the swelling of the plastic 

 contents (fig. 479, 1, 2, d). 

 There is thus a space on one | ^ 

 side between the lid and the 

 lower part of the female organ. 

 Then the mucous colourless por- 

 tion of the endochrome protrudes 

 from the aperture, and its colour- 

 less cellular membrane presents 

 a distinct lateral opening turned 

 towards the antheridium. When 

 the female organ has undergone 

 these further changes in its con- 

 tents, the lid of the antheridium 

 is completely detached, and 

 allows the upper cuneiform 

 ciliated spermatozoid to escape. 

 This spermatozoid, after mov- 

 ing around the female organ 

 for some time, enters the open- 

 ing. The spermatozoid reaches 

 the female globule, which is 

 then fertilised, and seems to 

 be absorbed in its substance. 



Fig. 479. 



After this the female globular body becomes more and more definite, 

 and finally is surrounded by a double membrane. 



In the cells of another Alga, called Sphseroplea annulina (fig. 480 

 a 6), there are produced stellate spores, very like the reproductive 

 bodies of Volvox stellatus. In spring' the contents of these spores 

 divide into two, then into four or eight parts, which become zoospores. 



Fig. 479, 1. Entire plant of (Edogonivm dliatwrn. a, Ordinaiy cells containing zoospores, 

 which ultimately escape and form new plants. 6, Sporangium, containing spores, c, 

 Androspore fixed on the sporangium, bearing at its summit an antheridium with a lid. d, 

 Setiform prolongation of the plant. Fig. 479,S2. Sporangium, with spores. S, Magnified, 

 c, Androspores bearing antheridium, with the lid at the top. d, Filament bending to the 

 side, so as to expose an opening into the spore-case, by which the spermatozoids enter. 



