PLATE 1 



EXPLANATION OP FIGURES 



All figures were drawn with the aid of a camera lucida, using a Zeiss 1.5 mm. 

 apochromatic objective and compensating ocular no. 12, with tube length of 

 160 mm. The drawings are reproduced natural size. They are taken from sec- 

 tions cut 5 M thick unless otherwise noted. 



1 and 2 Drosophila virilis Sturtevant mss./^ diploid metaphase, ovarian cell. 



3 D. ramsdeni Stt. mss., diploid metaphase, ovarian cell. 



4 Scaptomyza graminum Fall., diploid metaphase, spermatogonium. 



5 Same, ovarian cell. 



6 Same, haploid, second spermatocyte. 



7 Drosophila robusta Stt. mss., diploid, early anaphase, spermatogonium; 

 polar view showing separation of daughter halves of chromosomes. 



8 Same, ovarian cell; slightly earlier stage showing division of chromosomes. 



9 Same; slightly later stage. 



10 D. nebulosa Stt. mss., haploid, second spermatocyte prophase. 



11 Same, diploid, ovarian cell. 



12 Same, diploid, ovarian cell, two poles of anaphase; lower figures displaced 

 in order to compare the two groups (upper pole at left, lower at right); upper 

 figure a diagram showing the two anaphase groups as they appear in the sec- 

 tion. The small, spherical members are not evident. 



13 D. amoena Loew, haploid, late metaphase, second spermatocyte. 



14 Same, ovarian cell, prophase, diploid group. 



15 Same, diploid, metaphase, spermatogonium. 



16 Same, diploid, early anaphase, ovarian cell, showing separation of daugh- 

 ter halves of chromosomes. 



17 D. busckii Coq., diploid metaphase, ovarian cell. 



18 Same, haploid, first spermatocyte. 



19 D. ampelophila Loew, diploid metaphase, ovarian cell. 



20 D. dimidiata Loew, diploid, metaphase, ovarian cell. 



21 D. ornatipennis Will., diploid, ovarian cell, metaphase; this individual 

 apparently possesses three small, spherical chromosomes.^" 



22 Scaptomyza adusta Loew, diploid, metaphase, ovarian cell. 



19 See footnote 3, page 221. 



2° Apparently this case is comparable with that of the supernumerary 'm- 

 chromosome' described by Wilson ('10) in Metapodius, and results from non- 

 disjunction of the small chromosomes in one of the parents. LTnfortunately 

 only two or three good figures were found in my specimen (as is usually the case 

 in flies), and although these show the same features they are too few to be 

 demonstrative. It may be noted that the three chromosomes are associated 

 together in each of the figures. 



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