206 MONTGOMERY A STUDY OF THE CHROMOSOMES 



seem to be true to some extent, but not wholly correct for the following reasons. In a 

 large number of the species examined the chromatin nucleoli are regularly closely 

 apposed to the surfaces of true nucleoli. Now it seems probable that the true nucleoli are 

 masses of substances formed by the metabolism of the cell, probably waste substances 

 (Montgomery, 1899 b). When we find accordingly the mutual apposition of them to 

 chromatin nucleoli, it would be permissible to conclude that the chromatin nucleoli are 

 chromosomes which are especially concerned with nudeolar metabolism. And this I 

 think would be the correct interpretation. The chromatin nucleoli are in that sense de- 

 generate, that they no longer behave like the other chromosomes in the rest stages ; but 

 they would appear to be specialized for a metabolic function. Thus it might be that in 

 the Insects the chromatin nucleoli are those chromosomes which either exert a greater meta- 

 bolic activity than the other chromosomes, or which carry out some special kind of meta- 

 bolism ; and from this point of view they would certainly seem to be much more than 

 degenerate organs. As to their origin, compare the chapter on the " Number of Chromo- 



somes." 



Like the chromosomes, the number of chromatin nucleoli in the germ cells appears to 

 be a fixed one for the species. In somatic cells they are often more numerous than in the 

 germ cells, however, but that somatic difference will not be discussed in this paper which 

 concerns itself with the germinal cycle. 



(e) Occurrence. 



Chromatin nucleoli were found by me in all the Hemiptera examined, and I have 

 found them also in Coleoptem (Harpalus) and Orlhoptera (Gryllm, Ceutophilm). 

 McClung (1899, 1900) has described them in various Orthoptera, in some forms of which 

 they are larger than the chromosomes. Finally, my student, Miss Wallace (1900), has 

 found them in the sperm atogenesis of a spider (Agalenid). 



Accordingly they would seem to be present in the Insects and Arachnids, but are 

 apparently absent in the Crustacea, and I have shown (1901) that they are not present in 

 Peripatus. 



It is, however, quite possible that they will be discovered in other forms, if proper 

 attention is paid to them. The question of their ontogenetic origin will be considered 

 later (compare the section on the " Significance of the uneven number " of chromosomes). 



3. The Number of Chromosomes. 



The following table shows the number and valence of the chromosomes and chroma- 

 tin nucleoli in the Hemiptera examined, all of which has been explained in detail in the 

 chapter on " Observations." The abbreviation " univ" has been employed for " univa- 

 lent," and " biv." for " bivalent." 



