84 BULLETIN: MUSEUM OF COMPAEATIVE ZOOLOGY. 



should be re-examined, for if established this would throw great discredit 

 upon the theory of the individuality of the chromosomes. 



While many investigators seem to favor the view that the large "chro- 

 matin nucleoli" of germ cells have nothing to do with the formation 

 of the chromosomes, several assert that the chromosomes are derived 

 directly from their substance, and in some cases offer excellent evidence 

 to establish their conclusions. Thus we see that there are several im- 

 portant matters to be considered in discussing these chromatin-bearing 

 nucleoli. Among these are (1) their origin, (2) their structure, and (3) 

 their function and behavior during mitotic division. 



In considering the phylogenetic origin of the karyosphere and similar 

 chromatin-bearing bodies it has been seen that they are probably geneti- 

 cally connected with the karyosome composing the lower type of nuclei in 

 Protozoa and the similar structures (karyosome, Calkins; Binnenkor- 

 per, Rhumbler ; Chromatiukorper, R. Hertwig) found in the higher 

 types of nuclei in these unicellular animals. We shall now consider their 

 ontogenetic origin in metazoan cells. According to the views of different 

 authors they are either (1) of achromatic origin, produced by a chem- 

 ical change in the achromatin of the cell, or (2) of chromatic origin, 

 obtained from the chromosomes or chromatin reticulum of the nucleus. 



Concerning the bodies of achromatic origin, I shall say nothing here, 

 except that I believe it very improbable that chromatin which arises in 

 this manner — i. e. having no connection with the true chromatin elements 

 of the cell — should have any important significance in the succeeding 

 mitoses. This may account for the fact that in the maturation division 

 of many cells "nucleoli" staining like chromatin are cast out into the 

 cytoplasm, where they subsequently degenerate. Such a behavior has 

 been reported in a large number of metazoan cells (Hacker, '93, in Aequo- 

 rea; Wheeler, '95, in Myzostoma; Mead, '98, in Chaetopterus ; Griffin, 

 '99, in Thalassema, Zirphaea; and others). Such is probably also the 

 origin of the chromatic or nucleolar material which is discharged from 

 the resting nuclei into the cytoplasm, as reported by Balbiani, '93 (Geo- 

 philus, etc.), Jordan, '93 (newt), Calkins, '95 (Lumbricus), and others. 

 It is very improbable indeed that such an extrusion of nuclear substance 

 involves material derived directly from functional chromatin. 



Many investigators, however, assert the second alternative — i. e. that 

 the "chromatin nucleolus" is derived from the chromatin reticulum of 

 the nucleus. Among this number may be mentioned the following: 

 Blochmann, '82 (Neritina) ; Van Beneden, '83 (Ascaris) ; Van Bambeke 

 '85 (general) ; Carnoy, '85 (arthropods) ; Rabl, '85 (Salamandra) ; 



