No. 2.] 



HOMOLOGY OF THE CENTROSOME. 



439 



short, the history of the microsome and the filament runs in a 

 cycle. The microsome may be converted into the cytoplasmic 

 filament, and the filament, in turn, may give rise to a micro- 

 some. The cytoplasmic filament may be called the active phase, 

 and the microsome the inactive phase of the living cytoplasm. 



If we accept the general state- 

 ment that the microsome is more 

 commonly found at the junction 

 where two or more cytoplasmic 

 threads meet, then the problem 

 of the origin of the centrosome 

 in the centre of the aster is 

 greatly simplified. Foj- the centi-e 

 of the aster is the point wJiei-e the 

 greatest ntnnber of cytoplasmic 

 filaments meet zvith one another, 

 and the size of the microsome pro- 

 duce d at such a place must be 

 correspondingly lai'ge. In other 

 words, the microsome produced in 

 the centre of the aster is the 

 centrosome. 



The centrosome thus produced 

 gives rise in turn to a new set of 

 cytoplasmic fibres — the spindle 

 filaments. The view that the 

 spindle fibre originates from the 

 centre of the aster, and not from 

 the nucleus I have given elsewhere. 

 A glance at a series of caryokinetic 

 figures (Fig. 3 and Fig. 4) will 

 show that such is really the case. 

 The important fact that may be 

 observed in this connection, is that 

 those filaments produced by the 

 centrosome are the smooth fibres 

 which are free from varicosities, 

 at first. The observations of 



C" 



Fig. 6. The connective tissue 

 cells frofti the lung of Salamander. 

 C, centrosome ; N., Nucleus ; 

 Zk., "Zvvischenkorper." After W. 

 Flemming : IVeue Beitrdge ziir 

 Kenntniss der Zelle. Arch. f. 

 mikr. Anat. Bd. XXXVII, 1S91, 

 Taf. XXXVIII, Fig. 12. 



