ALGjE. 



13 



aplanogametangia generally grow out into short branches, which 

 lie close together and touch one another, the wall at the point 

 of contact is then dissolved (Fig. 39). Through the aperture thus 

 formed, the aplanogametes unite, as in the first instance, and 

 form a rounded zygote, which immediately surrounds itself with 

 a cell- wall. Vai-ious modifications occur ; compare Figs. 37, 39, 

 41, 43. 



The highest form of the sexual reproduction is the Egg- or 

 Oogamous fertilisation. The two coalescing cells are in the main 

 unlike each other in form as well as size. The one which is con- 

 sidered as the male, and is known as the spermatozoid (antherozoid), 

 developes as a rule in large numbers in each mother-cell (antheri- 



M 



FIG. 9. Fertilisation in the Bladder- 

 wrack (Fucus vesiculosus). 



dinm) ; they are often self- 

 motile (except in the Flori- 

 deas, where they are named 

 spermatici) , and are many 

 times smaller than the other 

 kind, the female, which is 

 known as the eg g - cell 

 (oosphere). The egg-cell is 

 always a motionless, spheri- 

 cal, primordial cell which can either float about freely in the 

 water, as in the Fucaceje (Fig. 9), or is surrounded by a cell-wall 

 (oogonium) ; generally only one oosphere is to be found in each 

 oogonium, but several occur in Sphceroplea (Fig. 10). The re- 



FIG. 10. Spltosroplea annulina. 



