n MUSCINE^— HEPATIC^— MARCHANTIALES 33 



Uppermost cells are often, although not always, extended into 

 a beak. The spermatozoids do not seem to differ either in 

 their method of development or structure from those of other 

 Hepaticse, but their excessively small size makes it extremely 

 difficult to follow through the details of their development. 

 When ripe the wall cells are much compressed, but are always 

 to be distinguished. 



Like the archegonia, the antheridia are sunk separately in 

 deep cavities, which are formed in exactly the same way. 

 Unlike the archegonia, however, the antheridium does not 

 nearly reach to the top of the cavity, whose upper walls are in 

 many species very much extended into a tubular neck, which 

 projects above the general level of the thallus, and through 

 which the spermatozoids are discharged. 



The Sporophyte. 



After fertilisation is effected the tgg develops at once a 

 cell-membrane and enlarges until it completely fills the cavity 

 of the venter. The first division wall is more or less inclined 

 to the axis of the archegonium, but approaches usually the 

 horizontal. The lower of the two cells thus formed divides 

 first \)y a wall at right angles to the first formed, but this is 

 followed in the upper half of the embryo by a similar division, 

 so that the embryo is divided into nearly equal quadrants. In 

 each of the quadrants a wall meeting both of the others at 

 right angles next appears (Fig. 6, C, III), and the embryo at 

 this stage consists of eight nearly equal cells. The next walls 

 are not exactly alike, but the commonest form is a curved wall 

 (Fig. 6, C) , striking two of the others, usually walls II and III, 

 and intersecting the surface of the embryo. This wall divides 

 the octants into two cells, which appear respectively triangular 

 and quadrilateral in section. By the next division the arche- 

 sporium is separated from the wall of the sporogonium. These 

 walls are periclinal, and by them a single layer of outer cells is 

 separated from the central mass of cells which constitutes the 

 archesporium (Fig. 6, B, D). 



At first the cells of the embryo are much alike, but as it 

 grows the inner cells increase in size and their contents become 

 densely granular, while the outer cells grow only in breadth, 

 and not at all in depth, assuming more and more a tabular 



