OF THE GEEM CELLS OE METAZOA. 



201 



other assumption can so well explain the maintenance of a constant number. The fact 

 that the chromosomes build up new substance at one stage, and give off waste 

 products atanother, does not invalidate our conclusion. Those who deny the maintenance 

 of chromosomal individuality, on the basis of a study of objects where the chromosomes 

 do not appear to be continuous from generation to generation, are not justified in conclud- 

 ing that there is never a maintenance of the individuality until they have examined the 

 positive cases. And since there have been shown to be positive cases, we must conclude 

 (1) either that in all normal mitoses of the germinal cycle the chromosomal individuality 

 is maintained, or (2) that, it- is preserved in some cases but not in others. The fact that 

 it has been demonstrated for some cases renders it probable that is maintained in all 

 eases, even though it cannot be demonstrated in all. 



2. The chromatin nucleoli. 



The term "chromatin nucleolus" was applied by me (1898) to the remarkable 

 chromatin element, in form like a, nucleolus but in behavior and staining reactions like 

 a chromosome, in the nuclei of spermatocytes of Euchistus (Pentatoma) ; the name was 

 given in order to denote this double similarity, though 1 fully realized that this structure 

 was in all essentials a modified chromosome. A special monograph (1899b) was devoted 

 by me to the true nucleolus (plasmosome, Ogata) of Metazoan cells; and in a lecture at 

 the Woods Holl laboratory (1898b) 1 classified the other "nucleolar" structures as 

 " karyosomes, which are merely thickened nodal points of the chromatin reticulum ; 

 further, what! shall term the ' cliroiiialin-nucleus ' [typographical error for ' chromatin 

 nucleolus'], which is found in certain spermatocytes; and then various structures 

 which stain neither like the true nucleolus nor the chromatin, and to which such terms 

 as ' Paramcleoli,' ' Nebennucleoli,' and ' Pseudonucleoli ' have been applied. It is 

 one of the most difficult <|iieslions to determine the nature and correspondence of the 



latter structures But from the cases studied by me, it would appear that 



some of these structures in Metazoa probably must be placed within the category of true 

 nucleoli, and be regarded as true nucleoli of a different chemical nature ; .... our 

 criterion of nucleoli probably should not be based as much upon chemical as morpho- 

 logical tacts." 



The chromatin nucleolus is a. modified chromosome, as both my earlier and the 

 present observations show. The term may have been injudiciously chosen, since I myseli 

 showed that it has nothing in common with a true nucleolus except: sometimes in the 

 form and in containing vacuoles. In its stead MeClung (1899) haa given the name 

 "accessory chromosome," and Paulmier (189!)) the name "small chromosome." But 

 McClung's term is not satisfactory in not being at all definite, and Paulmier's term is not 



