THE CELL AND ITS CONSTITUENT STRUCTURES. 153 



Taking leave of the centrosome for the present, we may 

 briefly glance at the structure and mode of origin of the 

 spindle. And here, too, we are confronted by an astonish- 

 ing amount of diversity in detail, accompanied by a sur- 

 prising degree of similarity in the final result. The most 

 complete form of spindle is that known as Hermann's 

 spindle, to which I have already alluded. Here the primary 

 fibres, which form a central strand, arise in the protoplasm 

 and have in the first instance no direct reference to the 

 nucleus at all ; but, by-and-by, from the poles of this central 

 spindle radiations extend through the rest of the cytoplasm, 

 and are directed in special abundance to the nucleus. The 

 chromosomes which are now in process of formation are 

 roped up as it were on to the central spindle, finally becom- 

 ing symmetrically arrayed around it. During the division 

 of the chromosomes and the divarication of their respective 

 halves to opposite poles the movement seems to be effected 

 by a contraction of the peripheral roping spindle fibres, the 

 central spindle merely serving as a kind of railroad along 

 which the chromosomes travel. 



There are, however, other instances in which the same 

 thing is effected, but the mechanism is less complete. In 

 the spore mother cells of Fegatella ^ the spindle is of a re- 

 markable form, probably owing in part to the peculiarly 

 compressed shape of the cell. The spindle is not formed in 

 the same way as in the Salamander, but it originates simul- 

 taneously at two points not quite 180 degrees apart. Thus 

 the chromosomes are at first grouped in an angle of the 

 spindle. The point which is of interest to us just now is 

 the fact that at the earliest stages there seem to be no fibres 

 which run continuously from pole to pole ; this condition is, 

 however, speedily reached by the fusion of a number of 

 fibres which meet half way between the two poles." Then 



1 Farmer, " Further Investigations on Spore Formation in Fegatella 

 Monica," Annals of Botany, vol. ix. 



- Driiner {Jenaische Zeitschr. f. Naturw., Bd. xxix.) asserts that in the 

 Salamander the central spindle begins as the result of a fusion of radia- 

 tions, such as occurs in Fegatella. This is contradicted by Meves {Archiv 

 f. Mikr. Anat., Bd. xlviii., p. 19), who upholds the view that they are con- 

 tinuous from the moment at which the two centrosomes begin to divaricate. 



