2l6 KATHARINE FOOT AND E. C. STROBELL. 



claim that the chromosomes are the cause rather than the ex- 

 pression of cell activities. 



We believe that the evidence we find in Enschistus, as well as 

 in Anasa ('07), is distinctly opposed to the interpretation that the 

 chromatin nucleolus of the resting first spermatocyte is a phase 

 of one or more of the chromosomes, but we shall reserve the pub- 

 lication of this evidence in huscliistns until we can control it by a 

 more complete comparison with other forms. In the present 

 paper we shall limit ourselves to the relatively simple question, 

 is the chromatin nucleolus a structure associated with the male 

 cell only, as claimed by McClung, or is it, as claimed by Wilson, a 

 chromosome received from the egg, which during the rest stage 

 appears in the form of a chromatin nucleolus ? 



Two chromatin nucleoli unequal in size have been demonstrated 

 by Montgomery ('98, 'or, '06) in the first spermatocyt.es of 

 several varieties of Euscldstus, including Euschistus variolaritts, 

 and Wilson ('05) has demonstrated these structures in other Hem- 

 iptera, naming them chromosome nucleoli, because he believes 

 them to be chromosomes. In describing them in Cccnus and 

 Lygcens he says : " Throughout the whole of the growth period 

 in Ccemis, and from stage e onward in Lygceus, at least one of the 

 idiochromosomes can always be distinguished as a compact, 

 spheroidal, intensely staining chromosome nucleolus and fre- 

 quently both idiochromosomes are distinguishable in this form 

 in all of these stages. ... It is clear beyond all question that 

 at least the large idiochromosome may retain its identity through- 

 out the whole growth period, with the small idiochromosome the 

 case is not so strong" (p. 389). Of Brochymena he says : " There 

 can be no doubt that when only one chromosome nucleolus is 

 present it is to be considered as a bivalent body arising by the 

 fusion or synapsis of the two idiochromosomes " (p. 392). 



In the resting first spermatocyte of Enschistiis variolarius the 

 chromatin nucleolus is the most deeply stained and conspicuous 

 structure in the cell (Photos I ro). As a rule, only one is present, 

 but quite frequently there are two, sometimes equal, but in most 

 cases, very unequal in size ; exceptionally we have found three, 

 or even four, nucleoli in the same nucleus. 



We roughly estimated the number of the nuclei with one or 



