136 ANTHEROZOIDS. [CH. X 



Within the cavity a number of spherical cells are seen, 

 and inside each of these is developed one of the male 

 elements known as antherozoids, motile organisms resem- 

 bling the spermatozoa of animals. The antheridium 

 bursts by the rupture of the lid-cell, and its contents, 

 the rounded cells, escape. The process of bursting only 

 takes place when the antheridium is wetted, as for 

 instance with rain or dew in a state of nature, or under 

 the coverglass in the laboratory. Water has moreover 

 a special effect on the rounded cells, which are rapidly 

 disorganised, and thus set free the antherozoids, which 

 swim about in the water. Each antherozoid (see fig. 61) 

 is a tapering rod bent into a corkscrew, and bearing at the 

 smaller end where the coils of the spiral are closer a 

 number of long cilia, by means of which it swims 1 . 



Antherozoids are found in certain water plants, for 

 instance in the stone- worts Chara and Nitella, and here 

 it seems a natural and fitting adaptation that the male 

 element, which has to find its way to the egg-cell, should 

 be a swimming organism. But that in a land plant the 

 male element should be forced to swim to the egg-cell is 

 remarkable. It seems only possible to explain it as an 

 inheritance from an aquatic ancestor; just as the gill- 

 clefts of the mammalian embryo are such inheritances. 

 Biologically the fact is of interest for it seems to throw a 

 light on the mode of life of the prothallus. We can 

 understand the advantage which the prothallus gains 

 from its habit of growth, clinging as it does to the soil 



1 Each antherozoid bears a protoplasmic vesicle of unknown function. 



