REPRODUCTION. 609 



independently, but they have been observed to conjugate 

 in pairs. Thus, like the microzoospores of Ulothrix, they 

 exhibit incomplete sexuality. The process of conjugation, 

 as described by Berthold, indicates that, though externally 

 similar, the planogametes are physiologically different. One 

 of them, namely, comes to rest and withdraws its cilia; the 

 other, remaining motile, approaches and coalesces with the 

 former. The planogamete which is passive in the process is 

 the female, the one which is active is the male. 



In Cutleria, another of the Phaeosporeae, the sexual diffe- 

 rence is more marked. To begin with, there are two kinds of 

 gametangia which are obviously different from each other: 

 the one consists of a large number of small cells, and produces 

 a large number of small planogametes: the other consists of a 

 relatively small number of large cells, and gives rise to a few 

 large planogametes. The sexual process, as described by 

 Falkenberg, consists in the coalescence of one of the small 

 planogametes with one of the large ones. The large piano- 

 gamete has but a short period of motility; it soon comes to 

 rest, withdraws its cilia, and rounds itself off, the hyaline 

 pointed end of the planogamete becoming the receptive spot of 

 the resting-cell, the spot, that is, at which the small piano- 

 gamete will coalesce with it. The large planogamete is clearly 

 female, and the smaller one male. 



In the Fucaceae the sexual reproductive organs are very 

 different from each other, and the gametes differ, not only in 

 size, but in that the female cell is not, whereas the male cell 

 is, a planogamete. The female gametes are, it is true, ex- 

 truded from the organ producing them, but they are not 

 motile. When the difference between the sexual organs and 

 cells is so well-marked as this, special terms are employed. 

 The female gamete is now called an oosphere, the male, an 

 antherozoid: the organ producing the oosphere is termed an 

 oogonium, and that producing the antherozoid, an antheridium. 

 Inasmuch as the female gamete is wholly passive, the sexual 

 process is termed fertilisation, the female gamete being said 

 to be fertilised by the male. The product of the sexual 

 process, the fertilised oosphere, is termed an oospore. 



v - 39 



