No. 2.] 



HOMOLOGY OF THE CENTROSOME. 



441 



of the spindle it is quite long, extending from the pole to the 

 equator of the spindle. 



If the spindle fibres do not run nearly parallel with one 

 another, as in Fig. 5, S, but converge to a focus' in the 

 middle plane of the caryokinetic figure, then these equatorial 

 microsomes will fuse into one solid body and give rise to a 

 " Zwischenkorper " (Fig. 6, Zk.). In other words, the 

 " Zwischenkorper " is an intercellular centrosome, produced 

 at the equatorial plane of the spindle in precisely the same 

 way as the ordinary centrosome. 



The present view further suggests a new explanation con- 

 cerning the nature of the centrosomes in the barrel-shaped 



Fiff. 7. 



X< 



Fig. 7. The division of the secondary embryosac-nucleus of Mojitropa 

 Hypopitys, X., Knob-like thickenings of the filaments composing the barrel- 

 shaped spindle. These thickenings are the '■^ polar microsomes" of the text. 

 After Strasburger, Zellbildimg tind Zelltheihmg; i88c, Taf. V. Fig. 134. 



spindle, as in the Ascaris (maturation-spindle), Spirogyra, Mono- 

 tropa (Fig. 7) and several others. In these forms the caryo- 

 kinetic spindle appears truncated at both ends. Instead of 

 the spindle fibres converging to a point as they usually do, 

 they terminate abruptly at a certain distance from the equa- 

 torial plane. The usual astral centre is wanting. If our view 

 of the centrosome be correct, we should not find it in such a 

 form of the spindle, but each filavicnt or a group of fezu 

 filaments ought to have a inici'osonie — a small, indcpentlent 

 " centrosome, ' ' as it zuere — at the extremities of the filafuetit or of 



