512 ' Edmund B. Wilson. 



the fate of the chromosome-nucleolus, differs entirely from them 

 in regard to its origin, concluding that it is derived from two of 

 the larger spermatogonial chromosomes. In the attempt to 

 reconcile these contradictory results (with both of which my own 

 are in disagreement) he is led to some speculative conclusions that 

 I think must be regarded as highly improbable. 1 



A careful study of all the intermediate stages, not only in Anasa, 

 but also in Alydus, Archimerus, and Chariesterus gives in point 

 of fact, evidence that I believe is quite decisive, that the small 

 central bivalent is not derived from the large chromosome-nucleolus 

 of the growth-period, and that the latter is nothing other than the 

 accessory or heterotropic chromosome, precisely as in the Orthoptera. 

 To the differences between the idiochromosomes and the m-chro- 

 mosomes already stated may therefore be added the fact that the 

 former, like the heterotropic chromosome, may form a single 

 chromosome-nucleolus during the growth-period, while this is 

 not the case, in the forms I have studied, with the m-chromosomes. 

 It may seem strange that Montgomery, after accurately tracing 

 the history of the heterotropic chromosome ("chromosome *") 

 in Protenor and showing its complete independence of the "chro- 

 matin-nucleoli" (m-chromosomes) was not led to suspect a 

 similar relation in the other forms. That he apparently did not 

 do so was doubtless due to his having failed to distinguish between 

 the m-chromosomes and the idiochromosomes, which latter bodies 

 he correctly identified (in'Euschistus, etc.) as the bivalent chromo- 

 some-nucleolus (or two separate univalents) of the growth-period. 



The entire independence of the large chromosome-nucleolus 

 and the m-chromosomes is most obvious in Alydus and Archi- 

 merus, partly because in both these forms the heterotropic 

 chromosome is at every period recognizable by its characteristic 

 size, partly because in Alydus certainly, and I believe also in 

 Archimerus the m-chromosomes frequently assume a compact 

 condensed form at a much earlier period than in Anasa; they can 

 therefore be recognized in addition to the heterotropic chromosome, 

 throughout the latter part of the growth-period, at a time when 

 the larger chromosomes are still in the pale, vague condition 

 characteristic of so many of the Hemiptera at this period. 



In Alydus pilosulus the first mitosis invariably shows seven 



'Gross ('04) pp. 481, 482. 



