272 BULLETIN OF THE 



(1.) A mural layer (Wandschicht), — the "nuclear membrane." 



(2.) A substance distributed through its interior, connecting with the mural 

 layer, and disposed in branching fibres, which do not exhibit any distinct reg- 

 ularity of arrangement (nuclear net, intranuclear network, or, better still, 

 intranuclear tressel). The fibres (Balken) of this tressel present thickenings 

 of variable form and number, — reticular nodes (Netzknoten). 



(3.) Genuine nucleoli, which lie usually in the thicker, occasionally in the 

 thinner, fibres of the network from which their substance diff'ers. In the living- 

 condition the nucleoli — often several, but generally only one or two — are 

 frequently not distinguishable. 



(4.) A pale substance, which fills out the remaining intermediary space, 

 and exhibits in the living condition no structure : — Zwischensubstanz of the 

 nucleus. 



Flemming especially insists upon the point that the nucleoli are not simply 

 thickenings of the tressel-work, and defends his position by the results obtained 

 in staining and decolorizing. It may be observed, however, that the process 

 of decolorizing would necessarily take substantially the course indicated, even 

 if the nucleoli were only concentrations of the tressel-work, since the removal 

 of coloring matter must, ceteris paribus, permit the bulkier portions of the 

 structure to remain longest in view. But this objection is anticipated by the 

 author when he emphasizes the fact that the Netzknoten (inclusive of nucleoli) 

 are often more intensely stained than their connecting fibres. " Die Netz- 

 knoten sind vielfach absolut, nicht bloss relativ nach ihrer Grosse, starker 

 gefarbt wie die iibrigen Theile des Netzes." But the very fact that the 

 Netzknoten stain intensely seems to me very unfavorable for the demonstra- 

 tion of a difference between the nucleoli and the tressel-work, for the 

 Netzknoten are defined to be simply thickenings of the tressel-work. 



Other conclusions from the results of staining are, that, since the nucleus is 

 alone stained, or at least more deeply than the rest of the cell, it must be dif- 

 ferent from the remaining substance of the cell, — therefore different from 

 " protoplasm." The staining of the nucleus affects all its parts, but the inter- 

 mediary substance less than either the network, its nodes, or the mural layer. 



In well-stained preparations the external limit of the nucleus is sharply 

 marked, so that a connection of intra- and extra-nuclear fibres is doubtful. 

 Flemming finds nothing to support the idea that the nucleus deports itself 

 in staining like the plasm of colorless blood-corpuscles or young cells. 



c. The KucLErs during Division. 



Introductory. 



As is well known, two fundamentally different views have been held 

 about the condition of the nucleus at the time of cell division. Accord- 

 ing to one, the nucleus, on account of its dissolution and the distribu- 

 tion of its substance through the common protoplasm, disappears before 



