732 



LECTURE XLI. 



nrp ^gng — arrSp-ffQtiia, and antheridia — arise on the vegetative body, in whirli tKo 

 nns^hpr es 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 oi-^ucu^ (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 fertiUsed 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 reproduction of Fuacs vesiculosus. A cell-lilanients bearing antlieridia ; B antiierozoids. / oogo- 

 nium Og witli paraphyses p ; // tlie outer membrane a of the oogonium lias burst, exposing tile inner one containing 

 the oospheres ; /// an oosphere which has escaped, and is surrounded by antherozoids ; V first division of the ferti- 

 lised oospore; /K young Fucus produced by the growth of the" latter. (After Tliuret— 5 X 330, the rest X 160.) 



typical cases of the Muscineae and "Vascular Crvptopfams, however, are approad itfl 

 by those A lgse which never produce more than one oosphere in an ooB ;onium.^ which 

 remamsjmmovable" within Jhe membrane of the oogonium^ and is fprtilispH_ hy the . 

 a ntherozoid s enterin g through a neck-like a p erture in it. 



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

 genus of non-cellular Algae, Va ucheria , common everywhere, figured on p. io8 (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 esqapes into the water, as shown on p. io8 at ^. The body B thus 



