l66 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 z3'gote 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, H, /, y). 



In Eudorina elegatis, a form closely related to Pan- 

 dorina, there is a striking difference in the size of the 



conjugating zoospores. In this form 

 Reproduction in • . ,, • . . ,, • u jj j 



„ , . sixteen or thirty-two cells are imbedded 



hudonna. . -^ 



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 tgg 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, A, 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 

 tgg cells (Fig. 8, D). A single antherozooid fuses with 

 each tgg 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 



