THE HISTOLOGY OF THE BLOOD OF LARVA OF LEPIDOSIREN PARADOXA, 297 
(2) Origin of Centrosome. 
The origin of the two centrosomes is very difficult to arrive at. I have seen 
only a very few corpuscles with a localised radial disposition of the reticulum in 
which there were not two centrosomes, either together in the same, or one in each 
of the adjoining sections of the series, and these few cases are difficult of interpretation. 
There is not a single clearly defined centrosome, but an area (fig. 3, Pl. I.) on 
which the radii converge. This is occupied by granules in every way similar to the 
microsomes. The extreme rarity of this stage, if it be a stage, shows that it must be 
a short-lived one, and that almost immediately the centre of activity is duplicated. 
It is clear that the centrosome or centrosomes described have no direct relationship 
to that of the previous division. The resting cells have no centrosome, and no 
eranules distinguishable from the microsomes which can be recognised as centrioles. 
Further, the new centrosomes do not appear where the old disappear, and therefore, 
unless on the purely theoretical assumption that the centrioles are scattered in 
the protoplasm, and though indistinguishable retain their identity,* to become the 
new focus or foci, the centrosome must be considered to appear de novo. ‘That 
this is actually the case is strongly supported by instances such as these figured 
on Pl. |. figs. 5 and 6, in which two centrosomes are seen so far removed from 
one another that it is hardly possible to believe that they have not appeared quite 
independently of one another. It is remarkable, however, that in later stages, when 
the centrosomes are very far apart, presumably successors of a stage such as figured 
(Pl. I. fig. 6), they are still single. I have seen no multipolar figures, and in such 
cases there is a suggestion that the chromosomes are forming themselves into two 
groups round the two asters. I have seen only a small number of such figures, but 
even the one or two I have seen seem to prove that the two centrosomes may appear 
independently ; and the fact that the independent centrosomes do not divide and 
form multipolar figures further suggests the possibility, in the absence of any stage 
in which a single definite centrosome can be confidently asserted, that the two 
adjacent centrosomes are independent from the first—that is, as definite stainable and 
recognisable foci. 
(3) Mistory of the Nucleus during Mitosis. 
It will not be necessary to deal in detail with the history of the chromatin as 
it presents only the well-known evolutions; a few points only require to be 
mentioned. 
The spireme thread is not beaded ; that is, there is no distinction between a linin 
basis and chromatin granules imbedded in it. The whole thread stains uniformly. 
dn this respect it differs from the thread seen in the prophases in the nuclei of the 
* Muves, Verhand. anat. Gesellschaft, 1902. 
