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XYII. — The Structure of the Nucleus. 

 By E. J. Sheppaed, F.E.M.S. 



{Bead June 18, 1913.) 

 Plate XXI. 



Before proceeding to the subject-matter of my paper, I quote a 

 few extracts from authorities on cytology in order to show what 

 are the current views as to the structure of the nucleus and its 

 limiting membrane. I then describe the results I have obtained 

 from observations carried out on vegetable and animal cells and 

 the conclusions to which these results lead, pointing to the neces- 

 sity for a considerable modification of the views hitherto held as to 

 the structure of these elements of the cell. 



Extracts. 



E. A. Schafer, Microscopic Anatomy, 1912, p. 36. 



Nuclear Membrane and Network. — All nuclei except those in 

 process of division appear to be bounded by a distinct membrane 

 formed mainly of basichromatin, but probably consisting also of 

 linin. This membrane forms a sharp division between nuclear 

 contents and cytoplasm. It was at one time thought that the 

 membrane is frequently incomplete and furnished with pores, or 

 even in the condition of a basket-work. This may sometimes be 

 the case so far as the chromatic portion is concerned, but the con- 

 dition is rare ; in nearly all cases of resting nuclei the membrane 

 appears in sections as a sharply-bounded line. On its inner sur- 

 face the membrane is connected with strands of the karyomitome 

 reticulum, which vary greatly in number and in thickness. These 

 form, as already stated, a network or spongework throughout the 

 interior of the nucleus, the trabeculee being sometimes equal and 

 regular; in others, and in the majority of cases, unequal in size 

 and irregular in distribution. Sometimes the trabeculte appear to 

 trend towards one pole of the nucleus. The material of which 

 these strands are composed is, in the main, like the nuclear mem- 

 brane, stainable by basic dyes, and in a nucleus thus stained their 

 nodes or junctions show out more strongly than the rest, so as to 



Oct. 15th. 1913 2 I 



