THE ARCHEGONIAT^E 



197 



like the oogonium of most Green Algae. The archegonium generally 

 consists of a single superficial layer of cells, and an axial row of 

 cells, of which the lowest one is the egg-cell. The upper part is the 

 Neck, the lower enlarged portion the Venter. At maturity the axial 

 row of neck-cells (" Canal-cells ") become disintegrated, and when 

 water is applied, these swell up and burst open the apex of the neck, 

 through which they are forced out, leaving a passage open to the 

 venter, within which lies the egg, ready for fecundation. 



The Antheridium. The antheridium (Fig. 158) is also multicel- 

 lular, but more variable in structure than the archegonium. It most 

 commonly is a stalked body, the upper part being composed of an 

 outer layer of sterile, often chlorophyll-bearing cells, and an inner 

 mass of sperm-cells. Within each of these a single coiled spermato- 

 zoid is developed. The body of the spermatozoid is derived mainly 



F. 



FIG. 158. Sphserocarpus cristatus. Development, of the autaeridium. A-D, median 

 longitudinal sections (X 450). E, an older one (X 225). F, spermatozoid (X 900). 



from the nucleus of the sperm-cell, while the cilia arise from a 

 special body, the Blepharoplast, which, in its position, recalls the 

 centrosomes of certain cells, but is found only in the later stages of 

 the sperm-cells. Like the walls of the canal-cells of the archego- 

 nium, the walls of the sperm-cells become mucilaginous, and when 

 the ripe antheridium is wet, the swelling of this mucilaginous mass 

 bursts open the antheridium and sets free the sperm-cells, from which 

 the spermatozoids are liberated by the complete dissolution of the 

 cell- wall. 



The liberated spermatozoids swim about actively in water and 

 make their way to the open archegonium, to which they are attracted 

 by substances ejected from it. This attractive substance in the Ferns 

 is malic acid. The .spermatozoids often collect in large numbers 

 about the mouth of the archegonium and several may make their 



