II MUSCINE^— HEPATIC^— MARCHANTIACE^ 33 



in most cases the next divisions, which are formed only in the 

 middle segments, are vertical, and divide the segments into 

 quadrants of a circle when seen in transverse section. 

 Occasionally a case is met with where the division walls are 

 inclined alternately right and left, and the divisions strongly 

 recall those of the typical Moss antheridium (Fig. 5, D). 



The separation of the sperm cells is brought about by a 

 series of periclinal walls in a number of the middle segments, 

 by which four central cells in each segment (Fig. 5, G) are 

 separated from as many peripheral cells. These central cells 

 have, as usual in such cases, decidedly denser contents than 

 the peripheral ones. 



The lower one or two segments and the terminal ones do 

 not take part in the formation of sperm cells, but simply form 

 part of the wall of the antheridium. The central cells now 

 divide with great rapidity, the division walls being formed 

 nearly at right angles to each other, so that the central part of 

 the antheridium becomes filled with a very large number of 

 nearly cubical cells. The divisions are formed with such 

 regularity that the boundaries of the original central cells 

 remain very clearly marked until the antheridium is nearly 

 mature. The basal cell of the antheridium rudiment in R. 

 glauca divides once by a horizontal wall (Fig. 5, B, D) and 

 forms the short stalk of the antheridium, which, however, is 

 almost completely sunk in the thallus. Between this stalk 

 and the central group of cells there are usually two layers of 

 cells, so that the wall of the antheridium is double at the base, 

 while it has but a single layer of cells in the other parts. The 

 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 Hepatic^, 

 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. 



D 



