1 68 BIOLOGICAL LECTURES. 



demonstrate how little unanimity exists in regard to it. Many 

 {e.g., Leydig, Klein, Retzius) regard it as merely a portion of 

 the chromatin reticulum, confusing it with the karyosome. 

 Macfarlane considers it the dynamic centre of the cell. Car- 

 noy distinguishes " nucleoles nucleiniens " {i.e., karyosomes), 

 "n. plasmatiques " {i.e., true nucleoli), " n. mixtes " (formed 

 by the union of the preceding two), and "n.-noyaux," which he 

 regards as nuclei within nuclei. Strasburger and others regard 

 it as a reserve supply of chromatin ; Hacker, as a secretion of 

 the chromatin, with possible excretory function. Flemming 

 considers it a nuclear organ, and as a " chemische Modification, 

 Vorstufe oder Doppelverbindung," of chromatin. Korschelt's 

 view is approximately the same as that reached by myself ; 

 namely, that nucleoli are formed as depositions of nutritive 

 substance. Rhumbler considers them to represent reserve ma- 

 terial, standing in some connection with chromatin ; Watase, 

 that they are metabolic products of the cell. Born concludes 

 that " die Nucleolen stehen in Beziehung zum individuellen 

 Zell-Leben, nicht zur Fortpflanzung." Further, there are nu- 

 merous modifications of these several views. 



As a matter of fact, the nucleolar phenomena are so multi- 

 form and complex, on a broad comparative view, that it is ex- 

 tremely difficult to decide the formation and nature of nucleoli. 

 The nucleolus is a structure upon which careful metabolic stud- 

 ies can be well pursued, but such investigation must be by the 

 comparative anatomical method as well as by the minute re- 

 search of a particular object. Neither method should be disre- 

 garded in morphological work, but the comparative would seem 

 to offer safer results. 



II. Other Nucleolar Structures. 



Besides the true nucleoli, which have just been discussed, 

 and the karyosomes, which in the strict sense of the term are 

 merely thickenings of the chromatin reticulum, there are found 

 in some cells structures which appear to resemble the chromatin 

 chemically, but which are not integral portions of the nuclear 

 network. Such, for instance, are the "double nucleoli" of 



