Lecture XX. 165 



closed cavity to a stellate form. The reduction of the volume of 

 the cavity so produced causes the inner mass of cells to burst 

 through the lid and ejects them from the antheridium. The 

 delicate walls of these latter quickly dissolve, and their contents 

 escape as spiral, ciliated, free-swimming masses of protoplasm. 

 They are the sperm-cells. 



The archegonia are formed exclusively on the cushion, close 

 behind the growing region of the gametophyte. They are flask- 

 shaped but much smaller and shorter than those of Marchantia 

 and of Funaria. Their body, or venter, is wholly embedded in 

 the cushion while the short curved neck projects from its under 

 surface and is directed obliquely backwards away from the grow- 

 ing region of the gametophyte. When the archegonium is formed 

 the cells composing the wall of its basal part enclosing the ovum 



FIG. 42. Aspidium filix-mas ; on left, antheridium discharging sperm-cells; 

 on right, an archegonium ready for fertilisation, x 250. 



do not differ from the surrounding cells of the cushion, and the 

 ovum appears as a spherical cell embedded among the superficial 

 thin-walled parenchymatous cells of the cushion. It is dis- 

 tinguished from its neighbours by its distinct nucleus, by its opaque 

 and finely granular protoplasm and by its poverty in chloroplasts. 

 The neck, which is composed of five rows of cells, projects from 

 the surface immediately over the ovum. The axial core vertically 

 over the ovum is composed of a single prismatic cell, the neck- 

 canal-cell. The four rows surrounding the neck-canal-cell each 

 consists of about five cells. The preparation of the ovum is 

 completed by the formation at its distal pole of a small lenticular 

 cell, the ventral canal-cell. Contact with water will now cause the 

 neck-canal-cell to swell up and burst open the distal end of the 

 neck, and the disintegration and solution of the neck-canal-cell 



