THE GERM-CELLS OF CICADA (TIBICEN) SEPTEMDECIM. 419 



This view is supported by the fact that in those stages where the 

 nucleoli re-appear, they usually lie close to each other (Figs. 

 43, 78), and in the strepsistene stages they are more loosely 

 granular in appearance than in the later stages. The later 

 increase in number of the nucleoli in the germinal vesicle stages 

 may be an expression of the increased metabolic activity of the 

 nucleus during this period. 



Wilson ('06) was unable to find chromosome-nucleoli in the 

 oocytes of Anas, Euschistus and other forms during the "contrac- 

 tion figure of the synaptic period" and he is inclined to doubt 

 the persistence of nucleoli in the oocytes homologous to those 

 found in the spermatocytes. As has been shown in Cicada, 

 it is quite probable that the sex-chromosomes go through synaptic 

 stages just like the autosomes and hence do not persist as compact 

 bodies in these stages as does the odd chromosome of the sperma- 

 tocytes. However, they may be present in the form of nucleoli 

 before and after the synaptic period. Foot and Strobell ('n) 

 have described a chromatin nucleolus in the oocytes of Protenor 

 which gives rise to two large idiochromosomes at the time of cell- 

 division. In Gelastocoris, Payne ('12) has described a chromatin 

 nucleolus which appears after the last oogonial division and 

 persists until shortly after synapsis. It later becomes reduced 

 in size and disappears, and Payne interprets it as having been 

 derived from the sex-chromosomes. The reason for the per- 

 sistence of the sex-chromosome in the spermatocyte and its non- 

 persistence in the oocytes during synapsis may lie in the fact 

 that in the former the odd sex element has no homologue with 

 which to pair, while in the latter the two sex-chromosomes are 

 homologous and synapsis becomes possible. However, with the 

 wide variations which these nucleolar structures exhibit in the 

 oocytes, it is not possible to make any generalization as to their 

 homology with the nucleoli of the spermatocytes. 



5. Discussion of the Chromosomes in Homopterans. 



(a) Review. The earliest work on the chromosomes of the 

 Hemiptera homoptera is that of Wilcox ('95) on Cicada tibicen 

 in which he states that there are 12 chromosomes in the spermato- 

 gonia and 24 "elements" in the spermatocytes. The work of 



