234 



ALG/E 



the conceptacle. The outer layer of the double wall of the oogone 

 bursts, the inner layer still continuing to enclose the oospheres in a thin 

 bladder-like membrane. In this form they escape from the conceptacle 

 through the ostiole into the surrounding water, where the remaining 

 membrane is also absorbed. In the meantime the antherids have become 

 detached, the inner layer of the double cell-wall having burst through 

 the outer layer, and collect in large numbers before the ostiole of the 

 female or of the bisexual conceptacles, forming orange-red masses which 

 are often caughf by the paraphyses which hang out from the ostiole, or 

 are left on the shore at low tide. On the return of the tide, or after 

 they have remained for a time entangled in the paraphyses, the inner 

 membrane of the antherid also becomes absorbed, and the antherozoids 

 escape at the same time that the oospheres become released from their 



FIG. 210. F. vesiculosus. A, branched hypha bearing antherids (x 160). B, antherozoids (x 330). 

 /, oogone, Og, contaiping eight oospheres ; /, unbranched hyphae. //, oospheres preparing to 

 escape ; a, outer, z', inner layer of cell-wall of oogone. ///, oosphere surrounded by antherozoids. 

 IV, V, stages in germination of oosperm (x 160). (After Thuret.) 



enveloping membrane. The antherozoids frequently collect round the 

 oospheres in such numbers that the motion of their cilia imparts to the 

 comparatively very large passive oosphere a rolling movement which lasts 

 for about half an hour, when they become absorbed into it and impreg- 

 nate it. The oospheres are receptive over their whole surface ; and, 

 although it has been calculated that the bulk of an oosphere is equal to 

 that of from 30,000 to 60,000 antherozoids, an oosphere can apparently 

 be fertilised by a single antherozoid. In this family the mode of repro- 



