THE ALG.E 



195 



(see Fig. 83, a). At first the antheridium, like other 

 cells in Fucaceae, contains a single nucleus. This under- 

 goes repeated division into two, until the total number 

 of sixty-four nuclei is reached. Each of these nuclei 

 now becomes the centre of a distinct cell, the contents 

 of the antheridium dividing up simultaneously into as 

 many protoplasmic bodies as nuclei are present. These 

 bodies become sperm- 

 atozoids, each of which 

 consists of protoplasm, 

 a nucleus,and a plastid; 

 the latter, however, 

 contains but little 

 colouring matter. The 

 spermatozoids are of 

 oval shape, and bear 

 two lateral cilia of 

 unequal length (see 

 Fig. 84, sp). The 

 antheridial wall is 

 double, and when the 

 organ is ripe the outer 

 membrane bursts at 

 the top, and the whole 

 contents, which may be already developed into sperm- 

 atozoids, but are still enclosed within the delicate inner 

 cell-wall, are expelled. 



The oogonia are single cells, of large size, seated on 

 the tissue at the base of the conceptacle (Figs. 82 and 

 85) ; they contain a great many plastids, and turn a very 

 dark colour as they become ripe. In each oogonium 

 there is at first a single nucleus, which divides suc- 

 cessively into two, four, and eight. The cell contents, 



V\ 



FIG. 83. Antheridia of Pelvetia. p, p, 

 hairs ; a, a, antheridia, some of which 

 are already emptied. Magnified about 

 260. (After Thuret and Bornet.) 



