while the sperms are 
produced in consid- 
erable numbers in an- 
theridia (Fig. 342). 
The oogonia and an- 
theridia are either de- 
veloped directly from 
the vegetative fila- 
ment (Hig. 343) or 
occur on special short 
branches (Fig. 342). 
The oogonium is a 
large, round struc- 
ture, usually with a 
projection, or beak, 
and is cut off by 
a wall. It contains 
a single egg, which 
when mature has only 
one nucleus. The an- 
theridium is a small, 
tubular branch which 
is usually curved at 
the time of maturity. 
The antheridium is 
cut off from the veg- 
etative filament by a 
cross wall. When 
the egg is mature, 
the odgonium opens 
at the beak. The 
mature  antheridia 
also open and in 
this way allow the 
sperms to escape. 
THALLOPHYTA 339 

Fia. 348. Vegetative filaments of Vaucheria 
bearing antheridia and odgonia 
First figure, antheridium and oégonium not separated 
from filament; second figure, odg’onium and anther- 
idium separated by cross walls; third figure, an- 
theridium after discharge of spermatozoids, egg 
fertilized. (x 145) 
These swim around and some reach an 
odgonium, where one of them fuses with an egg. The fertilized 
