$0 VAUCHERIA SESSILIS. 



case of zoospores the end of a nutritive filament is made 

 into a sporangium, which produces one large compound 

 zoospore, while special branches and sex-organs are 

 developed to produce the sex-cells. The oogonium 

 that produces the egg, and the antheridium that pro- 

 duces the sperms, are not only special organs for produc- 

 tion of these special bodies, but by their structure, and 

 their position with reference to each other, greatly 

 facilitate the process of fertilization. The division of 

 labor between nutritive and reproductive organs is well 

 established. Furthermore, the oospores are protected 

 by heavy walls as in Spirogyra, which gives greater 

 chances of successfully surviving severe changes in 

 temperature, moisture, etc. It is evident that Vaucheria 

 shows a decided advance in complexity. 



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