Nov., 1908.] The Centrosomes of Marchantia polymorpha. 385 



the minute structures desired. Accordingly, the observations 

 were made on these ten best sHdes. 



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 5'oung 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 



