732 



LECTURE XLI. 



organs — archegonia and antheridia — arise on the vegetative body, in which the 

 oospheres and antherozoids are developed. But even of this the first (of course 

 simple) cases are found in the Algae and Fungi. The vegetative body gives rise to 

 special organs, but of very simple structure, the oogonia, in which oospheres are 

 produced, and to others, antheridia (which would be better designated as spermo- 

 gonia) in which numerous antherozoids (zoosperms) are developed. Sexual organs of 

 this kind occur in a very perfect form in the various species oiFucus (Figs. 413, 414), 

 which are also worthy of mention here, because in some species two or several oospheres 

 are developed in one oogonium: these become surrounded by the numerous antherozoids 

 and fertihsed only after they have escaped from the oogonia, and are floating free 

 in the water, though they have no proper movement. In some Phycomycetes also 

 several oospheres are produced in one mother-cell, that is in one oogonium. The 



Fig. 414.— Sexual xa^mAnzimw ai Fuciis -'csiciilosus. ,J cell-filaments bearing antheridia £ antlierozo ds. j 

 nium Og with paraphyses / ; // the outer membrane a of the oogonium has burst exposing the inner one con 

 the oospheres! ///an oosphere which has escaped, and is surrounded by antherozoids I first diMsion of tin 

 lised oospore; /F young Fiuus produced by the growth of the latter. (After Thuret—.S X j30 the rest X i6o ) 



typical cases of the IMuscineae and Vascular Cryptogams, however, are approached 

 by those Algae which never produce more than one oosphere in an oogonium, which 

 remains immovable within the membrane of the oogonium, and is fertilised by the 

 antherozoids entering through a neck-like aperture in it. 



One of the clearest and best observed cases of this kind is met with in the 

 genus of non-cellular Algae, Vaucheria, common everywhere, figured on p. 108 (Fig. 

 107). On cultivating this Alga in a vessel of water at the window in the spring, it 

 reproduces itself at first only asexually. At the ends of the tubular branches, 

 which are abundantly supplied with chlorophyll, and which constitute the shoot of 

 this plant, a large portion of the protoplasm collects, and it is then separated off 

 by means of a transverse septum. This mass of protoplasm, which has pre- 

 viously contracted somewhat, then forces its way through an opening formed at 

 the tip, and escapes into the water, as shown on p. 108 zi A, The body B thus 



