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MONTGOMERY A STUDY OF THE CHROMOSOMES 



applicable to those cases where it is as large as the other chromosomes. Hence I con- 

 sider that confusion in terminology would be best avoided by retaining my original term, 

 " chromatin nucleolus." 



In my first description of the spermatogenesis of Euchistus (1898 a), I stated that 

 I could not find chromatin nucleoli in spermatogonia, and that one appeared for the 

 first time in the spermatocyte by a metamorphosis of one of the fourteen chromosomes ; 

 this was an error that I have corrected in the present paper, for in Euchistus, just as 

 Paulmier (1899) correctly described for Anasa, there are two chromatin nucleoli in the 

 spermatogonium, and these unite in the spermatocyte to form one bivalent one. And in 

 all the Hemiptera examined by me the larger chromatin nucleoli of the spermatocytes 

 are derivatives of chromatin nucleoli of the spermatogonia, except the remarkable 

 " chromosome x " of Protenor, to which we shall return. As far as I have been able to 

 determine, the chromatin nucleoli are always halved in the mitoses of the spermatogonia. 



(a) General Characteristics. 



The chromatin nucleoli are morphologically chromosomes, undergoing division in 

 mitosis like the other chromosomes, but differing from them in the rest stage by preserv- 

 ing a definite (usually rounded) form. There is also another difference which is of great 

 use in their study : by the use of the double stain of Hermann, saffranine and gentian 

 violet, the chromosomes proper stain red only in mitosis and violet in the rest stage, 

 while the chromatin nucloli stain red in the rest stage also, and so can be sharply dis- 

 tinguished from the chromatin of the chromosomes.* Thus the chromatin nucleoli of 

 the Hemiptera seem to retain at all stages the stain characteristic for the substance of the 

 chromosomes when in the height of mitosis. In the Hemiptera examined the true 

 nucleoli never takes this red stain, but take the violet, so that they may in this way be 

 easily distinguished from the chromatin nucleoli.f With iron-hrematoxylin staining 

 the chromatin nucleoli stain more intensely than the chromosomes in the rest stage ; but 

 with this stain the true nucleoli generally stain deep black like the chromatin nucleoli, 

 so that it is far less satisfactory than the preceding method for differentiating these two 

 structures. With the triple stain of Ehrlich-Biondi-Heidenhain, the chromatin nucleoli 



* The only exception to this staining reaction was found in the spermatocytes of Hygotrechus, where in the rest 

 stage the chromatin nucleoli always take the violet stain. 



t However, in cells of many other Melazoa I have found that the true nucleoli show a particular eleetivity for 

 the saffranine, so that chemical reactions are not tests for true nucleoli ; nucleoli may differ chemically from one 

 another, even in the same cell at the same stage, or at different stages, and no better case of this may be mentioned 

 than the ovocytes of the growth period of Gryllui. In the Hemiptera the true nucleoli are generally much larger 

 than the chromatin nucleoli, more or less irregular in outline, and they usually occupy a more or less central position 

 in the nucleus (though I have mentioned two or three exceptions), while the chromatin nucleoli in the spermato- 

 cytes are generally in contact with the nuclear membrane. 



