THE ALGAE 



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these densely branched structures. At first the antheridium contains a 

 single nucleus, but this is rapidly increased by division until sixty-four 

 are formed. Around each nucleus a membrane is formed, enclosing a small 

 quantity of protoplasm and a single orange chromoplast ; thus sixty-four 

 antherozoids are formed. Each is pear-shaped and has two lateral flagella, 

 one forward and one backward. They are unequal, with the shorter flagellum 

 forwards, contrary to the general rule among the lower Phaeophyceae. The 

 orange-coloured chromoplasts give 

 a bright colour to the mass of an- 

 therozoids which escape through 

 the ostiole. 



The antheridium, like the 

 oogonium, has a multiple wall, 

 though its layers are not so clearly 

 defined. The outer wall opens 

 apically and releases an oval inner 

 sac, containing the antherozoids, in 

 which they emerge through the 

 ostiole of the conceptacle. This 

 inner sac then swells and opens at 

 its ends, and the antherozoids swim 

 out into the sea water. 



The oospheres and antherozoids 

 are liberated with a quantity of 

 mucilage at ebb-tide and are 

 picked up by the advancing edge 

 of the flood-tide, and it is here 

 that fertilization takes place. The 

 membrane around the antherozoids 

 bursts when they have been libe- 

 rated from the conceptacle, and 

 they swim off by means of their 

 flagella. The antherozoids soon "^ig. i^z.-Fmijs serratm. A series of stages in 

 '= 11- ^^^ early development 01 the irond irom a 



seek out an oosphere, and im- fertilized zygote. 



mediately attach themselves to its 



surface in large numbers. They attach themselves by the tips of the 

 anterior flagella and the movements of the posterior flagella cause 

 the oosphere to rotate in the water, with its attached swarm of males. 

 Eventually one antherozoid penetrates the oosphere and its nucleus 

 travels inwards through the cytoplasm and fuses with that of the 

 oosphere. The resulting zygote immediately secretes a wall which pre- 

 vents penetration by any other antherozoid and becomes an oospore. 

 The wall of the oospore is mucilaginous and fixes it to the substratum 

 before growth begins. After twenty-four hours it begins to divide, the 

 nucleus dividing first, followed by the laying down of the first cell wall 

 between the daughter nuclei. This wall is invariably at right angles to the 



