FILICALES 



343 



but it does not open except in presence of external fluid water. This 

 causes swelling of the mucilaginous walls of the spermatocytes, and 

 increased turgor of the cells of the wall. The tension is relieved Ijy 

 rupture of the cell covering the distal end, and the spermatocytes are 

 extruded into the water ; in this the cells of the wall assist by their 



Fig. ;8+. 



I, an attenuated male prothallus of Xcphrodium Filix-nias. 2-5, stages of de\"elop- 

 ment of the antheridium. 6, 7, ruptured antheridia. S, a spermatozoid liif^hily 

 magnified, (.\fter Kny.) 



swelling inwards, and consequent shortening (Fig. 2S4, 6). The 

 spermatocytes thus extruded into the water which caused the rupture, 

 soon show active movement, and the spermatozoid which had already 

 been formed within each of them escapes from its mucilaginous 

 sheath, and moves freely in the water by means of active cilia 

 attached near one end of its spirally coiled body (Fig. 2S4, 8). 



The archegonium also originates from a single superficial cell, and 

 grows out so as to project from the downward surface of the thallus. 



