PLATE 4 



EXPLANATION OF FIGURES 



68 Musca domestica, diploid, metaphase, ovarian cell. 



69 Same, somewhat disarranged. 



70 Same, ovarian cell, early prophase, entire or almost entire nucleus. 



71 Same, nucleus not entire. 



72 Same, late prophase, nucleus almost entire. 



73 Phormia regina, haploid, metaphase, X-containing second spermatocyte. 



74 Same, Y-containing group. 



75 Same as 73, but slightly later, showing division of chromosomes. 



76 Same, first spermatocyte, early anaphase, polar view, showing reduction 

 division; note separation of X and Y (small pair). 



77 Same, diploid, spermatogonium, late metaphase showing division of 

 chromosomes. 



78 Same, diploid, ovarian cell, early prophase. 



79 and 80 Same, slightly later stage, nuclei entire, or nearly so. 



81 and 82 Sarcophaga tuberosa serraceniae, haploid, second spermatocyte, 



83 Same, first spermatocyte. 



84 Same, side view, showing separation of X and Y at the reduction division. 



85 to 88 Same, diploid, spermatogonia; two small members are X and Y. 



270 



