MALE GERM-CELLS. 



137 



The mode of origin of the mother-cells differs considerably in different 

 ferns, but in all cases is essentially as follows : An ordinary cell on the 

 . lower side of the prothallium swells and forms a hemispherical or dome- 

 shaped projection, which is soon separated by a partition from the original 

 cell (Fig. 72). Further divisions then follow in the dome-shaped cell such, 

 that a central cell is left, surrounded by a 

 layer of peripheral cells (Fig. 73). By re- 

 peated divisions the central cell splits up 

 into the spermatozoid mother-cells (Fig. 71). 

 Within each mother-cell the proto- 

 plasm arranges itself in a peculiar 

 spiral body, the spermatozoid, which 

 is the male germ-cell. 



When the mature antheridium is 

 moistened, the peripheral cells swell 

 and thus press out the mother-cells 

 and spermatozoids (Fig. 74). The 

 latter escape from the mother-cells and swim about very actively 

 in the water. They appear as naked single cells, of a peculiar 

 corkscrew shape, and bear upon the liner spirals numerous ex- 

 tremely active cilia (p. 31), by 

 which they are driven swiftly 

 through the water. 



The Archegonia, or female 



FIG. 73. (After Hofmeister.) 

 Later stage in the development 

 of an antheridium of Pteris ser- 

 rulate, p, peripheral cell; c, 

 central cell from which the 

 spermatozoid mother - cells 

 arise. 



Fro. 74. (After Luerssen.) Bursting of 

 the antheridium and escape of the 

 spermatozoids. an, antheridium ; m.c, 

 spermatozoid mother-cells; sp, sper- 

 Tnatozoids. 



FIG. 75. (After Strasburger.) Mature 

 archegonium, showing the oosphere 

 (o), the neck (n), and mucus (m) is, 

 suing from the mouth of the canaL 



