42O ELMER L. SHAFFER. 



Stevens ('050, '056) and of Morgan ('08, '09) on the Aphids 

 and Phylloxerans has dealt mainly with the problem of sex 

 determination. It was found that only spermatozoa bearing the 

 sex-chromosome are functional and consequently only females 

 are produced from fertilized eggs. Males are produced partheno- 

 genetically from eggs which during the maturation processes 

 reduce the chromosome number to one half the somatic number; 

 hence there is only one sex-chromosome remaining in the male. 

 Stevens ('06) and Boring ('07, '13) have studied the chromosomes 

 of over 20 species of Homopterans mainly in relation to sex 

 determination. Kornhauser ('14) has made a comparative study 

 of the chromosomes of two species of Enchenopa in which he 

 describes parasynapsis and pre-reduction. 



In all the Homoptera studies thus far with one exception, the 

 sex-chromosomes consist of but a single (X) element which 

 persists as a chromosome nucleolus through the growth stages 

 of the spermatocyte and passes, undivided to one pole of the 

 first maturation spindle. The only exception to this is that 

 described by Kornhauser ('14) in Enchenopa binotata in which 

 there are two sex-chromosomes (XY). These behave very much 

 like the autosomes in the growth stages of the spermatocyte, 

 becoming resolved into synaptic threads and pairing in synapsis 

 much as the autosomes do. In the preleptotene stages the sex 

 pair is found persisting as nucleoli. In the strepsistene stages, 

 when the chromosomes become more diffuse and lightly staining, 

 the chromatic nucleoli again appear by a condensation of the 

 threads representing the sex pair. It will at once be noted that 

 this behavior of the sex pair in Enchenopa resembles the behavior 

 of the two chromatic nucleoli which I have described in the 

 oocytes of Cicada and I am, therefore, led to believe that the 

 chromatic nucleoli of the oocytes are homologous to the chromo- 

 some-nucleolus of the spermatocytes. 



A common characteristic of the diploid chromosome complexes 

 of many Homopterans is the usual presence of a pair of large 

 rod-shaped chromosomes (A A pair of Cicada). Stevens ('06) has 

 shown these in Aphrophora, and Boring ('07) has figured these in 

 many of the Homoptera that she has studied. Kornhauser ('14) 

 had described them in two species of Enchenopa that he has 



