VAUCHERIA 433 



the fertilized ovum, and fitting closely within the 

 wall of the oogonium. 



2. An increase in the size and number of the oil 

 globules : no cell-division takes place. 



Y. The reproduction by means of zoogonidia may 

 readily be observed in specimens grown under favour- 

 able conditions in water : a considerable mass of the 

 Alga is to be placed in a porcelain bowl, in water, and 

 exposed in a window : after a few days, numerous small 

 plants of Vaucheria will be found floating on the 

 surface of the water, or disposed along the submerged 

 surface of the bowl: these have resulted from vegeta- 

 tive reproduction by zoogonidia. In order to see the 

 process observations must be made in the early morning, 

 or else the culture must be kept in the dark till shortly 

 before the observations are to be made. Shortly after 

 dawn (or soon after the specimens have been exposed 

 to light) some filaments may be seen with a lens to 

 have dark -coloured and slightly swollen ends : these 

 are about to form zoogonidia : mount some specimens 

 without a cover-slip, taking care to avoid injuring 

 them ; and examine under a low power : observe 



1. The swollen end of the filament, with dark, densely 

 aggregated protoplasm, surrounding a vacuole. 



2. The transverse septum dividing the swollen end 

 from the rest of the filament. 



If such specimens be kept under observation the 

 escape of the zoogonidium may be observed : the 

 following points are to be specially noted 



1. Various changes in the protoplasmic body and 

 vacuole, terminating in the formation of a transparent, 

 and radially striated, outer protoplasmic coat (ecto- 



F F 



