Nov., 1908.] The Centrosomes of Marchantia polymorpha. 
385 
the minute structures desired. Accordingly, the observations 
were made on these ten best slides. 
The nuclei of the antheridial cells are only 2-3 microns in 
diameter and all the cell structures are, therefore difficult to see 
unless one has good natural light, good slides, a good microscope, 
and good eyes. 
In my preparations, I found centrosomes in the antheridial 
cells of all stages. In the very early or incipient stages of the 
antheridium, the cells are somewhat larger but not so clear as in 
the last stages. The staining must, therefore, be very favorable 
before many details can be seen. It is not always easy to deter¬ 
mine the generation of any given set of cells. Nevertheless, one 
can come to a fairly good approximation and the exact stage is 
not of especial importance. The final division and the one 
preceding can of course be determined without difficulty. 
When nuclear division begins, cytoplasmic radiations appear 
at opposite sides of the nucleus. These asters have very dark- 
staining centers. These centers are the poles of the future 
spindle. Their appearance is shown in figures 1, 5, and 22-24. 
Figure 1 is from a very young antheridium, figure 5 is a great 
grandmother cell or an earlier stage, while figures 22-24 are 
spermatozoid mother cells in the final process of division. In 
the later stages the asters are not developed to any extent while 
in the earlier generations they are very conspicuous. The same 
is true for the mother star stage as will appear from an examina¬ 
tion of the figures. The most beautiful asters and centrosomes 
were observed in mother star stages of great grandmother cells 
(Figs. 10-13). The centrosome is often surrounded by a hyaline 
zone, the attraction sphere, and the aster is a prominent dark- 
staining structure forming a cloud-like halo (Figs. 11, 12). 
In the daughter star stage the centrosome appears elongated 
or somewhat double, being probablv in the first stage of division 
(Figs. 4, 14, 15, 20). 
In the later stages of the division of the spermatazoid mother 
cells to form the two spermatids, no doubling of the centrosome 
was observed (Figs. 31-40) although it becomes elongated and a 
double nature is probably shown by the development later of the 
two flagella. 
The centrosome appears to begin to enlarge somewhat even 
in the grandmother cells and in the last division, which is diag¬ 
onal as Ikeno discovered, the cells become comparatively clear 
and the centrosome enlarging still more is thus especially con¬ 
spicuous. As reported by others, the chromosomes were found 
to be eight in number in the gametophyte (Fig. 25). 
As stated above, after the final division the centrosome 
becomes elongated and appears as an oval, dense, dark-staining 
body from which the flagella develop. It is evident that this 
