Chrontosomal Variations in Earwigs 229 



reorganization a chromosome much smaller than the others can be seen. 

 Figure 31 shows this small chromosome. This stage seems to be later 

 than that shown in figure 30 where the small individual lies against 

 the large chromosome. Conditions similar to these figures are very 

 common in the cysts showing the rest stage. No great difference was 

 found in the sizes of the chromosomes in the metaphase plates showing 

 12 chromosomes (figs. 13, 14) but in figures 15 and 16 showing metaphase 

 plates with 13 chromosomes one small chromosome can be seen. This 

 would indicate that the attached univalent was much smaller than the 

 other chromosomes and this difference in size should make it noticeable 

 at once when it became detached. On the basis of size the small body 

 appearing in the rest period (figs. 30, 31) seems to be the univalent 

 chromosome. Further study shows this small element behaving in the 

 prophase of the second spermatocyte division as the other chromosomes. 

 This seems to warrant the conclusion that the small univalent that 

 disappeared prior to the first spermatocyte division became attached 



34 35 



Figs. 29-35. (29), Late anaphase showing chromosomes in condensed mass; (30 

 and 31), rest stage between first and second spermatocyte divisions showing very 

 small chromosome; (32 and 33), second spermatocyte metaphase with 12 chromosomes; 

 (34 and 35), same showing 13 chromosomes. 



to one of the autosome pairs and remained attached until the re- 

 organization of the nucleus in the telophase of the first spermatocyte. 

 Since the specimens were collected fairly late in the season some of 

 the testes were filled with mature spermatozoa and many of the others 

 had few cysts with cells in division. Although all the stages described 

 above could be traced in many specimens there were a few that had 

 several cysts in metaphase that permitted a large number of counts 

 per individual. A description of one typical specimen with several 

 cysts in metaphase might be of interest here. Specimen 40 seems to 

 be of interest in this connection. Only one clear count of the 

 spermatogonial metaphase could be made. It showed very definitely 

 25 chromosomes. The description of the growth period given above could 

 be applied to this specimen (figs. 5, 6 and 8) although very few prophase 

 groups similar to figures 11 and 12 were found. Here all of the 14 

 clear metaphase counts in the primary spermatocyte showed 12 chromo- 

 somes. The one cyst in the rest stage between the first and second 

 spermatocyte divisions showed clearly many stages the close associa- 

 tion of the small chromosome and the large one similar to figures 30 



