300 DR THOMAS H. BRYCE ON 
I am obliged, therefore, to conclude that, as a recognisable structure, the centrosome | 
disappears completely when mitosis is over, and that, in the absence of any proof that 
a contained centriole divides in the telophase to survive to the next generation, the 
centrioles also disappear as such, whether they be twin centrioles or a group of centnokay 
that could be supposed to persist. 
Since the demonstration by Writson,* following the earlier observations of Morean, 
that centrosomes arise de novo in the echinoderm egg during artificial parthenogenesis, a 
conclusion such as I have come to will seem less improbable than it would have some 
years ago. 
(c) Interpretation. 
As stated above, the conclusion was arrived at that the meshwork seen in the fixed 
corpuscles represented a protoplasmic framework in the living cells. Certain features 
of the resting cells, and certain appearances observed during mitosis, suggest that the 
protoplasm is. of a specially viscous or ductile nature. The early history of the 
achromatic figure and of the centrosome preclude the application to this particular case 
in sensu stricto of either the fibrillar hypothesis (Van BenepeEn), or of the doctrine of 
the organic radu (HerpENHAIN). Both involve a structure of the resting cell which 
does not exist in the erythrocytes. In the conceptions of RuumBLER,t however, I find 
room for a free formation of the centrosome ; and the interesting feature of this case is, 
that the theoretical conditions of his model of cell division are fulfilled more closely 
perhaps than in any hitherto described. 
The general reticulum is in the resting cell centred on the nucleus. It is under 
some degree of elastic tension, but the focus of that tension is not a centrosome, and | 
therefore the conditions are not such as represented in HrrpenHain’s{ model. On the 
appearance of the centrosomes, the reticulum begins to show a new disposition. It is _ 
now centred on these bodies, and round them is converted into radially directed — 
threads. This radial arrangement of the reticulum is probably brought about by 
the withdrawal of the mesh walls circumferentially disposed into those radially dis- | 
posed to the centrosomes. 
Apart altogether from the why and wherefore, the centrosomes and their radiations 
are a manifestation of a tendency of the protoplasm to retract or concentrate itself at 
two focal points. The first effect of the retraction is the rounding up of the corpuscle; | 
the second effect is the separation of the centrosomes. 
When there are two centrosomes at some distance apart (PI. I. figs. 5 and 6), the | 
reticulum becomes converted into a symmetrical aster round each. When they lie close | 
together, the asters are not symmetrical, for between them the protoplasmic material is | 
limited, and is in large measure retracted on to the opposing centres. The progressive | 
condensation or retraction of the threads on the outer sides being thus in excess of that | 
* Arch. f. Entwickelungsmek., Bd. xii., 1901. + Ibod., Bd. iii., iv., xvii. 
t Ver. anat. Gesell., Berlin, 1896. Arch. f. Entwickelungsmek., Bd. i. 
