166. FOOT-NOTES TO EVOLUTION. 
may remain dormant for a long time, thus tiding over 
a period of drouth, the winter months, etc. After this 
resting period, if brought under suitable conditions of 
moisture, the outer wall of the zygote ruptures, the con- 
tents escape in the form of a large swarm spore, which 
swims about for a time and then divides into the sixteen 
cells of a new colony (Fig. 7, A, 7, /). 
In Ludorina elegans, a form closely related to Pan- 
dorina, there is a striking difference in the s¢ze of the 
conjugating zoospores. In this form 
sixteen or thirty-two cells are imbedded 
together in a common spherical gelat- 
inous mass. The asexual mode of reproduction is the 
same as in Pandorina, just described, each cell of a 
colony being transformed by successive divisions into a 
new colony of sixteen or thirty-two cells which becomes 
free from the parent colony. The sexual mode presents 
a difference in that the colonies differentiate into two 
sorts termed male and female. In the female colonies 
the cells become transformed into spherical egg cells or 
oospheres without further division. In the male colo- 
nies, however, each cell divides into sixteen or thirty- 
two antherozooids, minute, elongated cells, each pro- 
vided with two long cilia projecting from its anterior end 
(Fig. 8,4, B,C). These remain slightly united together 
in bundles and, escaping from the parent colony, swarm 
for a time in the water together. Coming in contact 
with a colony of oospheres, they break apart, penetrate 
into the gelatinous envelope, and find their way to the 
egg cells (Fig. 8, ). A single antherozooid fuses with 
each egg cell, and the conjugated pair form a resting 
zygote around which a cellulose wall forms, and from 
which, after a certain period of time, a new colony of 
sixteen or thirty-two cells develops. 
A third stage in the differentiation of the conjugating 
Reproduction in 
Eudorina, 
