164 BIOLOGICAL LECTURES. 



the cytoplasm, which, becoming caught by mantle fibres of the 

 spindle, would be passively divided. Or, to state the case differ- 

 ently, it would appear that in mitosis equal division of the 

 nucleolar substance does not appear to be effected. 



Judging from my observations on the reduction divisions in 

 Anasa and EucJiistiis (Hemipterous Insects), and in Piscicola, 

 as well as on the ovogonic divisions of Linens, there appears to 

 be no good evidence that the nucleolar substance takes part in 

 the production of the spindle fibres. Yet such a view is held 

 by Strasburger and others, based upon the generally simul- 

 taneous disappearance of nucleolus and appearance of spindle 

 fibres. Thus in Euchistiis, the object in which this question 

 has been most thoroughly studied by me, in the spermatogonia 

 the central spindle connecting the centrosomes is formed at 

 some distance from the nucleus, and the pole rays, also of cyto- 

 plasmic origin, may be seen before the nuclear membrane has 

 disappeared ; while the mantle fibres are undoubtedly of nuclear 

 origin, as are the interchromosomal threads, both being pro- 

 duced by a gradual change of position of the linin threads 

 before the disappearance of the nuclear membrane. However, 

 it may be going too far to conclude that in no objects are the 

 spindle fibres formed of nucleolar substance. But in view of 

 the evidence showing that nucleoli are masses of passive mate- 

 rial, and that the spindle fibres are (temporary.?) states of pre- 

 existing living matter, one would be justified in concluding 

 that in all probability there is no genetic connection between 

 spindle fibres and nucleoli. 



Another point may be briefly referred to. The central 

 spindle corpuscles (" Zwischenkorperchen " of Flemming, by 

 whom they were first described) may by certain methods be 

 caused to stain like nucleoli. The general consensus of opinion 

 is that these corpuscles are thickenings of central spindle fibres 

 or of connecting fibres. But might not in some cases undis- 

 solved portions of nucleolar substance come to lie in the equator 

 of the spindle, and there be confused with true " Zwischen- 

 korper".? This question is of interest with regard to the older 

 view of Strasburger, that the nucleolar substance forms the 

 cell plate in plant cells, and consequently the cell membrane. 



