426 Wilson . — Spermatogenesis in the Bryophyta. 
and Mnium are produced from the nucleus before each division. A small 
body is cut off from the nucleolus, which at first lies free within the mem- 
brane, but soon passes into the cytoplasm, becoming rod-like, and by con- 
striction and division producing two centrosomes. These pass to opposite 
sides of the nucleus, and finally occupy the poles of the spindle. Before the 
final division in Mnium after the centrosome has been separated off, the 
nucleolus divides into two bodies of equal size, one of which passes into 
the cytoplasm and there disappears, the other persisting as the nucleolus. 
Although the production of bodies from the nucleolus in the last two 
divisions in the antheridium can be confirmed in the case of Mnium hornum , 
the examination of a large number of preparations leads to the conclusion 
that these bodies do not pass outside the nuclear membrane as long as the 
latter is present. As already described, the cytoplasm of the spermatogenic 
cells is very regular in structure and is free from deeply staining 
granules, and it is exceedingly unlikely that any body equal in size even to 
the smaller of those cut off from the nucleolus would be constantly over- 
looked 'after its passage through the nuclear membrane. At the same time 
it may be pointed out that the size of the smaller body produced before the 
final division is considerably greater than that usually associated with 
a centrosome. 
The importance of the separation of a body from the nucleolus at these 
divisions will be discussed later, but it maybe stated here that a similar pro- 
cess has been observed in cells found in the neighbourhood of the stem apex. 
In these cases the cells in question are of considerable age, and it is probable 
that no further divisions would in any case have taken place. 
In the spermatogenic cells the further history of these bodies has not 
been ascertained with certainty. During the following prophase a number 
of chromatin masses appear scattered throughout the nucleus and the nuclear 
membrane disappears (PI. XXXVII, Fig. 9) ; at this stage neither the nucleolus 
nor the bodies in question can be distinguished. It could not be ascertained 
whether the latter take part in the formation of the spireme, but judging from 
the course of events in the reduction division it is probable that they do not 
function in this way. The spireme soon appears as a close network, and 
a little later the individual chromosomes can be distinguished. From the 
frequency of its occurrence the latter stage is of considerable duration, and 
in this respect the later antheridial divisions differ from those already 
described in the archesporium, where this condition is not well marked and 
is rarely found. The chromosomes are of the usual form, but are frequently 
curved and intertwined (Fig. 10), and, in consequence, it is often rather 
difficult to ascertain their number. As before, no difference in the size 
of the six chromosomes was observed. The metaphase is quite normal, and 
is quickly passed over. As a rule the axis of the spindle coincides with the 
long axis of the cell, but owing to the irregularity in the shape of the cells 
