Herposteiracece 



71 



the thallus which are devoid of bristles. These cells grow in size, 

 assume a globular form, and become filled with starchy and oily 

 material. One oosphere is produced, which is motile, having four 

 cilia, and is expelled from the oogonium by the rupture of the 

 upper portion of the wall. The antheridia are small cells usually 

 developed at the ends of the filaments and branches ; they are 

 frequently colourless and are considerably smaller than the ordinary 

 vegetative cells. One or two antherozoids are produced in an 



Fig. 19. A, Herposteiron pilosissima (Schmidle) nob., from Wimpole Park, Cam- 

 bridgeshire. B D, H . confervicola Nag. ; B and C, from Bradford, W. Yorka. ; 

 D, from Kichmond Park, Surrey (x450). a, aplanospore. 



antheridium. These are pear-shaped bodies with four cilia and 

 two pulsating vacuoles, and are much smaller than the zoogonidia. 

 They escape into a hyaline vesicle which soon becomes diffluent 

 and sets them free. The antherozoids move about very rapidly, 

 but the movements of the oosphere are very feeble. The Herpo- 

 steiracese is the only family of the Chgetophorales in which the 

 fertilization of the oosphere takes place outside the oogonium. 

 Little is known concerning the development of the oospore. 



Genus Herposteiron Nag., 1849. [Aphanochcete A. Br., 1851 ; 

 Berth., 1878 ; Huber, 1892.] The thallus is filamentous, creeping 



