OBSERVATIONS ON STRUCTURE OP CELLS AND NUCLEI. 317 



and distribution of the protoplasmic fibrillar substance varies 

 in the cells of different kinds. 



R. Hertwig^ and Biitschli- distinguish, like Scliwalbej 

 the former a ' nuclear substance' from a ' nuclear juice/ the 

 latter a ^nuclear matter' from a 'nuclear fluid.' The ^nuclear 

 matter' of Biitschli comprises the nuclear membrane, the 

 nucleolus and a fibrillar stroma ; the latter in some instances 

 extends and a radial manner from the nucleolus. 



E. van Beneden^ saw a fine protoplasmic reticulum in the 

 large axial entoderm cell of Dicyema, which (reticulum) 

 exhibited slow spontaneous movements. In the nucleus of 

 the ripe ovum of Asterocanthion ruhens, v. Beneden 

 observed within the nuclear membrane and besides the 

 nucleolus a delicate network of a finely granular substance, 

 ' Nucleoplasma,' including several ' Pseudo-nucleoli.' Also 

 the germinal vesicle of the ripe ovum of rabbit contains a 

 minute network. 



Arndt (' Uber den Zellkern. Sitzung. d. medicin. Vereins 

 zu Greifswald/ Nov., 1876), distinguishes in the nucleus a 

 homogeneous ground substance and elementary globules ; 

 the former possesses a reticular structure and encloses in its 

 meshes the latter. 



W. Flemming^ made very important observations on the 

 structure of the nuclei found in the membrane of the 

 urinary bladder of Salamandra maculata. This author, to 

 whose paper I shall have to refer more minutely hereafter, 

 saw a very delicate and dense network of fibres uniformly 

 pervading the interior of the nucleus and attached to the nu- 

 clear membrane. This network — ' Geriistformige Structur' — 

 was seen by Flemming in the nucleus of all cellular elements 

 of the bladder of Salamandra — epithelial cells, connective- 

 tissue cells, migratory cells, unstriped muscle-cells, nerve- 

 cells, endothelial cells and blood-corpuscles. 



The clearness and extent of the observations of this author 

 leave no doubt that the network in tlie nucleus represents a 

 definite and pre-existing structure. Although this is to a 

 certain extent questioned by Langhans' as regards the fresh 

 cells of the human decidua serotina, Flemming's assertions 

 cannot be, I think, in the least shaken, considering that he 

 observed the above structure, not only after the use of 



1 'Morpholog, Jahrbiicber,' vol. ii. 



^ L. c, vol. X. 



3 ' Bulletins de I'Academie roy. de Belj?.,' 2 ser., t. 41, No. 1 and No. G 

 1876. 



" " Beobaclitungen liber die Beschaffenbeit des Zellkernes," 'Arcliivf. 

 Mikrosk. Anatomie,' Bd. xiii, p. 693 and following. 



* Laughans, 'Centralbl. f. Medic. Wissensch.,' 1876, N. 50. 



