112 



N. M. STEVENS. 



nature, and the members of the pair are in about the position 

 which they assume in the spindle. Throughout the growth 

 stage the composite pair of chromosomes is found, more or less 

 condensed, but always distinguishable from the remainder of the 

 chromatin against the nuclear membrane, twisted or coiled or 



20 



FIGS. 1417. Anopheles punctipennis, first spermatocyte metaphase. X=the 

 unequal pair. 



FIG. 1 8. Anaphase. 



FIGS. 19 and 20. Culex pipiens, first spermatocyte metaphase and anaphase. 



FIG. 21. Anopheles punctipennis, second spermatocyte metaphase. 



FIG. 22. Spermatid nuclei. All figures same magnification 2,000. 



knotted into such shapes that it is usually impossible to dis- 

 tinguish the equal and unequal pairs of which it is composed. 

 Prophase stages are evidently much briefer than in Culex, 

 for it was difficult to find any clear figures Fig. 13 shows the 

 composite heterochromosome pair (x) and the other two chro- 

 mosomes not yet separated into their parallel components. 



