1892.] Phenomena and Development of Fecundation. 291 



and female, although from external appearances we cannot 

 recognize the difference between them. When the zoospores 

 or planogametes are discharged from the mother cell, they do 

 not differ by any morphological character. The females do not 

 attract the males, but they swim around in the water and pass 

 each other unnoticed. After a time, however, sex becomes 

 manifest, and notably in accordance with the anabolic character 

 of the female. Certain ones of the planogametes become motion- 

 less, draw in their cilia and assume a rounded shape (li.tr. 1 ( .». 

 a-c). The female character of such cells is shown by the 

 attraction they exert on the active males which collect about 

 them in great numbers (a hundred or more), clustering at 

 one side in a half circle. The anterior filament of each male 

 is directed toward the female cell and is kept continually mov- 

 ing back and forth over it, the object being, it is thought, to 

 provoke in the female planogamete genital excitation (tig. 

 19, d). After continuing to stroke the female for a time, one of 

 the male planogametes leaves the circle and approaches the 

 female, with which it gradually fuses, and fertilization is com- 

 plete (fig. 19, e-h). 



In the pond scums (Spirogyra, etc.), the reproduction of 

 which is probably familiar to all, the filaments appear exactly 

 alike, but the female character of one is shown by the cells 

 of that filament containing all the spores resulting from the 

 conjugation. 



In Cutleria, mentioned above, the difference is manifested by 

 the size of the conjugating cells, but as we noticed, both male 

 and female are still motile. 



In the common rock weed, (Fucus— fig. 21), the differentia- 

 tion becomes marked by the external forms of the sexual cells. 

 The female cells are large and motionless, while the male cells 

 are becoming more intensely male by a comparative decrease 

 in size and increase, if anything, in vigor. By the vigor of 

 their motions they give the oosphere, around which they col- 

 lect in great numbers, a rotary motion for a time until it is fer- 

 tilized. 



In the mosses (fig. 18) and ferns, discussed above, we reach 

 a complete and highly developed state of sexuality, probably 

 more complete than in the higher flowering plants. 



