243 
found. The second series of divisions are vertical and are formed 
only in the middle segments and divide each into the quadrants 
of a circle as seen in cross section. (Fig. 7,b.) The separation 
of the sperm-cells is brought about by a series of periclinal walls 
by means of which four central cells in each segment are separated | 
from as many peripheral ones. (Fig. 7, b, c.) The upper and 
lower segments do not seem to take any part in the formation of 
Sperm-cells, the upper usually being prolonged into a beak, while 
the lower one forms the base of the antheridium. 
The lower of the two divisions of the antheridial mother-cell 
divides usually by three transverse walls to form a stalk. This 
stalk may be a single row of cells, or a vertical division may take 
Place, making a double row. (Fig. 6, b.) 
The contents of the central cells become much denser than 
those of the outer ones. The former begin to divide actively, the 
walls being formed at right angles, thus making a large number 
of nearly cubical sperm-cells. 
From the time the antheridium first becomes recognizable, thers 
is a rapid growth of the cells immediately surrounding it. These 
grow up about the antheridium, which thus becomes sunk in a 
deep cavity whose walls are extended into a tubular neck, project- 
ing above the general level of the thallus, and through which the 
Spermatozoids escape. 
The wall-cells of the antheridium are very large and distinct, 
and fill the whole cavity between the body of the aaeieericiiere and 
the wall of the cavity. (Fig. 6, a.) 
The complete development of the spermatozoids was not fol- 
lowed, but there was nothing to indicate any variation from what 
has already been described in other liverworts. The nucleus 
Shows the usual flattened form, after the last division of the cen- 
tral cells, and the sperm-cells remain in pairs. The full grown 
Spermatozoid shows one and one-half complete coils ; the two cilia 
are longer than the body, and the vesicle is plainly evident. 
Explanation of Plate 268. 
Fig. 1. Male plant with antheridial branches ;  3- 
Fig. 2. Vertical longitudinal section; apical cell; two very young antheridia 
X 400, 
