THE ALG.E 



155 



female plant either near or actually upon the oogonium 

 (Figs. 66 and 69, A). The androspore surrounds itself 

 with a cell-wall and germinates. The plant which it 

 produces is always of very small size ; it may consist of 

 a basal vegetative cell with one or more antheridial cells, 

 or the vegetative part may be absent, and the whole 

 dwarf male be reduced to an antheridium only. In the 

 antheridial cell, or in each 

 of them if more than one 

 be present, two sperm- 

 atozoids are produced. 

 They escape by a lid-like 

 opening of the anther- 

 idium, and make their way 

 to the oogonial aperture 

 (Figs. 66 and 69, A). 

 Like the ordinary sperm- 

 atozoids, they move by 

 a crown of cilia ; they 

 are also able to help 

 themselves along by the 

 contractions of their 

 whole body. The same 

 power of contraction is of 

 service when the oogonial 

 opening is reached, for 



the entrance may be much narrower than the body of 

 the spermatozoid, which can only pass through by 

 accommodating its form to the size of the passage. 



The act of fertilisation now takes place ; the 

 spermatozoid comes into contact with the protoplasm 

 of the ovum, and the two cells unite. The details of 

 fertilisation have been exactly followed in (Edogonium ; 



FIG. 69. A, fertilisation of (Edogon- 

 ium ciliatum ; <$, dwarf male 

 plant from which a spermatozoid 

 has escaped ; sp, the spermatozoid 

 in contact with the ovum, $. Mag- 

 nified 350. B, a single spermatozoid 

 showing cilia. Magnified 350. C, 

 germination of the oospore in Bul- 

 bochcete, showing the contents divided 

 up to form four zoospores. Magnified 

 250. (After Pringsheim.) 



