296 DR THOMAS H. BRYCE ON 
The first evidence of the onset of mitosis is the formation of a bulging of the central 
nuclear portion of the corpuscle on one side. In this projection are seen in the vast 
majority of cases two centrosomes lying side by side, and close to the surface of the — 
corpuscle, and remote from the nucleus (Pl. I. fig. 4). Each centrosome is the focal point 
of far-reaching radiations, which are clearly directly continuous with the reticulum of the 
corpuscle. They have every appearance of being simply a radially disposed portion of 
the general network. The centrosomes are not connected directly by intervening fibres, 
In fig. 4, Pl. I. an appearance seen in that, as well as other corpuscles, is suggested. On 
the left of the nucleus the meshes of the network appear drawn out towards the site of 
the centrosomes, and the radial fibrillee can be traced far out forming the walls of the - 
meshes of the network. This appearance is transitory. In the next stage (Pl. I. fig. 8, 
Pl. IV. fig. 34) the lateral wings have been drawn in, and the corpuscle has become 
spherical. The radiations are confined to one pole of the cell, the centrosomes remain- 
ing near together and close to the surface. 
(1) Structure of Centrosome. 
The structure of the centrosome varies according to the character of fixation 
and the manner of staining. In iron hematoxylin sections the appearances depend 
on the degree of abstraction of the stain. When much of the stain is left, the body 
is a very large one, and the black colour is even continued out along the radial 
fibrille. When the decoloration is carried far, there is a much smaller dark point 
in the centre of a halo staining red in preparations counterstained with eosin. The 
fibrillee spring from the circumference of this halo (Pl. II. fig. 13). This is clearly — 
an instance of concentric decoloration, and the black spot is not a true centriole in — 
Boverrs* sense. I have not been able to demonstrate a single such centriole or — 
pair of centrioles at any stage of mitosis, but frequently the centrosome has the — 
appearance of a grey spot, containing a group of centrioles. A slightly lobed 
appearance of a solid centrosome points to the same structure, even though no F 
separate granules are to be made out. The question arises whether this is a 
‘fragmentation’ of the centrosome (Boveri)* or the true structure. 
With the other dyes used the centrosome is not so vividly differentiated as with 
iron hematoxylin, but in view of the tendency of that stain to mask a finer structure 
by remaining lodged between the smaller elements, a truer picture is perhaps obtained 
by their use. In methylene blue and eosin sections the centrosome is a red area 
occupied by fine granules of the same size as the microsomes, but darker in colour, 
having a neutral tint—an appearance very possibly due to their being massed together. 
In the same way in triacid preparations the centrosome is yellow, with brownish yellow 
eranules. 
* Zellen-Studien, Heft iv., “ Uber die Natur der Centrosomen,” 1900. 
