11 MUSCINE^—HEPATICJE—MARCHANTIALES II 



remains of the cell contents not used up in the formation of 

 the spermatozoid. 



When the ripe sexual organs are placed in water their 

 outer cells absorb water rapidly and become strongly distended, 

 while the central cells, i.e., the canal cells of the archegonium, 

 and the sperm cells, whose walls have become mucilaginous, 

 have their walls dissolved. The swelling of the mucilage 

 derived from the walls of the central cells, combined with the 

 pressure of the strongly distended outer cells, finally results 

 in the bursting open of both archegonium and antheridium. 

 In the former, by the forcing out of the remains of the canal 

 cells an open channel is left down to the ^gg, which has been 

 formed by the contracting of the. contents of the lowest of the 

 axial cells. In the antheridium the walls of the sperm cells 

 are not usually completely dissolved at the time the anther- 

 idium opens, so that the spermatozoids are still surrounded 

 by a thin cell wall when they are first discharged. This soon 

 is completely dissolved, and the spermatozoid then swims 

 away. The substance discharged by the archegonium exer- 

 cises a strong attraction upon the spermatozoids, which are 

 thus directed to the open mouth of the archegonium, which 

 they enter. Only a single one actually enters the tgg, where 

 it fuses with the egg-nucleus, and thus effects fertilisation. 

 The tgg immediately secretes a cellulose wall about itself, and 

 shortly after the fusion of the nuclei is complete the first 

 segmentation of the young embryo takes place. 



The origin of the sexual organs is from a single cell, but 

 the position of this cell varies much. In the thallose Hepaticae 

 it is a superficial cell, formed from a segment of the apical cell 

 either of a main axis or of a special branch. In most of the 

 foliose Hepaticse and the Mosses, the apical cell of the shoot 

 becomes itself the mother cell of an archegonium, and of course 

 with this the further growth of the axis is stopped. The 

 antheridia in the foliose Hepaticae are usually placed singly 

 in the axils of more or less modified leaves, but in most Mosses 

 the antheridia form a terminal group. Mixed with the sexual 

 organs are often found sterile hair-like organs, paraphyses, 

 often of very characteristic forms. In the foliose Hepaticse 

 and most Mosses, the archegonia are often surrounded by 

 specially modified leaves, and in the former there is also an 

 inner cup-like perichastium formed from the tissue surrounding 



