NATURE OF NUCLEUS-CORPUSCLES. 115 



fall from side to side in each distended corpuscle ; and Schultz * appears 

 to have recently advanced a similar opinion. But Henlef remarks that 

 he has never been able to witness this phenomenon, and he considers the 

 nucleus of blood-corpuscles, as also those of mucus-corpuscles and 

 epithelium-cells, to be attached to the inner surface of the cell-wall. 



The nature and composition of the nucleoli, or nucleus-corpuscles, still 

 remain obscure. Henle J is doubtful whether what have been described 

 as nucleoli may not be merely spaces in the interior of the nucleus. 

 He thinks that this view of their nature is supported by the circum- 

 stance of no apparent chemical difference being perceived between them 

 and the nuclei ; agents which destroy the one, invariably destroying the 

 other also. Vogt, although he admits the real existence of nucleoli, 

 usually of a vesicular character, yet agrees with Henle in regarding them 

 as unessential elements of a cell. He states that when they appear, it is 

 only at a late period of the cell's life, and that shortly after their forma- 

 tion they usually assume a vesicular character, and as they enlarge are pro- 

 bably developed into cells at the expense of the nucleus which they 

 gradually destroy. Kolliker,|| however, entertains an entirely different 

 view of the nature and importance of the nucleoli. In his opinion, the 

 nucleus ought to be regarded as a primary nucleated cell, and the struc- 

 ture usually called a primary cell as a secondary cell. In the formation 

 of such primary cell (the nucleus of other writers) he believes that a 

 round, dark, apparently homogeneous substance is first developed in the 

 formative fluid. Around this body, which by him is regarded as the 

 nucleus, by others as the nucleolus, the wall of the primary cell is gra- 

 dually developed. Occasionally two, more rarely three, and still more 

 rarely four, dark particles are found in a single primary cell (nucleus). 

 Whatever may be the number, one at least is invariably found in every 

 such cell up to a certain period of its growth. When single, the particle 

 is situated on the wall of the cell ; when there are several particles, they 

 may occupy a similar situation, or be free in the cavity of the cell. 

 Occasionally one or two particles apparently identical with these are found 

 also among the contents of the secondary cells (or primary cells of other 

 writers). They have all the appearance of being composed of oil or fat. 

 Indeed, they appear to be identical with the elementary granules com- 

 monly found in the cytoblastema, and which Henle (as well as others) 

 describe as minute vesicular-looking particles of fat. And it is difficult 

 to determine in what respect they differ, and why Henle should discard 

 the use of the term nucleoli ; for, as will be presently shewn, he admits 

 the importance of the elementary granules in the first formation of cells. 

 Kolliker confirms Vogt's statement that the nucleoli are sometimes deve- 



* Hcnle's Allg. Anat. p. 192. f L. c. J Op. cit. p. 151. 



Entwickelungs-geschichte der Geburtshelferkrote, p. 118. 

 II Entwickelungs-geschichte der Ccphalopoden, p. 149, 



