PLATE 12" 



EXPLANATION OF FIGURES 



All of the figures are from Oncopeltus fasciatus excepting 7 and 8, which are from 

 Lygaeus bicrucis. Enlargement 2250 diameters. 

 1-3 Spermatogonial metaphases. Oncopeltus. 

 4-5 Metaphases from ovarian cells. 



6 Spermatogonial metaphase. Lygaeus. 



7 Metaphase of first spermatocyte-division. Lygaeus. 



8-13 Metaphases of first spermatocyte-division in polar view. Oncopeltus. 

 14-17 Metaphases of same in lateral view, showing the sex-chromosomes near 

 the center. 



18 Early anaphase of same division, showing all the chromosomes. The two 

 at the right and the one at the left have been drawn displaced so as not to confuse 

 the central group. 



19 Later anaphase, showing approach of the sex-chromosomes. 



20 Slightly later stage, showing the sex-chromosomes in contact at each end 

 of the spindle. 



21 Slightly earlier anaphase, from a smear-preparation, showing all the chro- 

 mosomes. The sex-chromosomes already in conjugation at each pole. 



2° All of the figures of plates 1 to 7 have been drawn as far as possible with the 

 camera lucida, though of course at so great an enlargement it has been necessary 

 to finish much of the finer detail freehand. Many of them are the work of Miss 

 Mabel L. Hedge, to whose skill and painstaking accuracy especial acknowledg- 

 ment is due. In many cases (as indicated in brackets) the same objects are shown 

 by photographs on plates 8 to 9. It should be added that some of the finer details 

 appear less clearly in the reproductions of these photographs than in the original 

 negatives. 



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