242 PART IV. CLASSIFICATION. 



spcrmatium : the spermatia surround themselves with a proper 

 wall at the time of fertilisation. 



The sexual organs. In those Algse in which the sexual cells are 

 similar, and the sexual process is isogamous, the sexual organs are 

 gametangia. In many cases they are unicellular and undifferen- 

 tiated : thus, when the gametophyte is unicellular (e.g. Desmidiese, 

 Diatomacese) the cell itself constitutes the gametangium ; and in 

 some multicellular or coenocvtic forms (e.g. Zygnemeee, Hydrodic- 

 tyon, Confervoidese) the gametangia are simply ordinary vegetative 

 cells or coenocytes. In some isogamous Algse, however, the game- 

 tangia are differentiated as lateral appendages, and are multi- 

 cellular, as in the Phseosporese ; in Cutleria it is even possible to 

 distinguish the male from the female gametangium. 



When the gametangium is unicellular or coenocytic, it usually 

 gives rise to a number of gametes ; but in the Conjugates a single 

 gamete is formed. When the gametangium. is multicellular, 

 each cell usually gives rise to a single gamete ; but in the male 

 gametangium of Cutleria 2-8 gametes are developed in each cell. 



The female organ, the oogonium, is in all cases unicellular or a 

 coenocyte ; in Sphseroplea it is undifferentiated, retaining the form 

 of a vegetative segment of the incompletely septate plant ; in 

 most cases it is more or less spherical in form, and in some species 

 of Coleochsebe it is prolonged at the apex into a delicate tube, the 

 trichogyne. It opens, in most cases, by the absorption of the wall, 

 at a point opposite the receptive spot of the oosphere when that 

 is present; but in others (e.g. Volvox, Chara) it remains closed. 

 In the former case the spermatozoid enters by the aperture : in 

 the latter, it bores its way through the wall of the oogonium which 

 becomes mucilaginous at its exposed surface. The oogonium of 

 the Fucacese ruptures and sets free the contained female cell or 

 cells. Usually a single female cell (oosphere) is formed in an 

 oogonium, by the rejuvenescence of its protoplasmic contents ; but 

 in various Fucaceae, the protoplasm divides to form two, four, 

 or eight oospheres, and in the coenocytic oogonium of Sphaeroplea 

 there are several oospheres. 



The female organ of the Rhodophycese, the procarp, is some- 

 times unicellular (e.g. Nemaliese), but more commonly multi- 

 cellular. It is in nearly all cases prolonged into a trichogyne, the 

 basal portion being termed the carpogonium. The trichogyne re- 

 mains closed. The protoplasm of the procarp does not undergo 



