OF MICRO-ORGANISMS. 85 



contracts, and presents at its free end a slight pro- 

 tuberance, which allows the zoospore to fix itself upon 

 an immobile point; as to the rear flagellum, it slips 

 back upon the posterior part of the body which it 

 encompasses, and finally disappears. When the fe- 

 male zoospore has become motionless, the male zoo- 

 spores, hitherto indifferent, are seen to make towards 

 it and to surround it in a half-circle; the number of 

 zoospores that thus meet, is quite considerable; it 



frequently exceeds a hundred 

 (fig. 10). They let their second 

 flagellum float loosely behind 

 them, while they all direct their 

 anterior filament towards the fe- 

 male cellule; this filament they 

 draw back and forth over the 

 Fig. io. sexual reproduc- body of the female cellule; they 



tion of the Ectocarpus silicu- r , i r r 1 



losus. Female zoospore sur- perform upon it real acts of feel- 



rounded by male zoospores. ,1 i r i_ i_ 



ing, the object of which is evi- 



dently to provoke in the female zoospore a genital ex- 

 citation, as what follows will prove. It happens at 

 times that several of the male zoospores quit the 

 ranks and make off; they are immediately replaced by 



others who employ 

 their filaments in a 

 like manner, to stroke 

 the female. Finally, 

 upon the expiration 

 of a certain time, 



Fig. ii. Sexual reproduction of the Ecto- One of the ZOOSpOrCS 

 carptis siliculosus. Successive stages of the i fVi 



copulation of a female zoospore with one of the leaves trie 



male zoospores. i j i 



cle and approaches 



the female. The two zoospores unite; after having 

 presented the series of changes marked in the figure, 



