(EDOGONIUM 



47 



average cell of a thread, is formed by repeated divisions 

 of parts of the thallus. The contents of these small 

 cells are transformed into ciliated zoospores, which, 

 although like ordinary zoospores in appearance, are 

 smaller; in fact, they are intermediate in size between 

 vegetatively produced zoospores and spermatozoids: 

 because of their special function they have been named 

 " androspores " (Gr. aner, andros, a man). The andro- 



Fia. 16. — CEdogonitom ciliat€m. 



X 350. 



an. Escaping andiospore ; 



$ , an oogonium. 



Fig. 16. — CEdooonium ciliatum. 



A, J , dwarf male plant from 

 which a spermatozoid has been 

 liberated ; $ , egg-cell which is 

 being entered by the sperma- 

 tozoid, sp. ; B, a spermatozoid. 



spores escape from the mother-cells in which they were 

 formed (see Fig. 15), swim about for a brief period, and 

 then settle on a female thallus, either upon the swollen 

 oogonium or very near it. Thus settled, each andro- 

 spore develops into a minute plant of a few cells. In 

 one or more of these cells spermatozoids are developed 

 to the number of two per cell; they eventually escape 

 by the opening of a caplike lid as shown in Fig. 16, and 



