PLATE I 



EXPLANATION OF FIGURES 



All figures, with the exception of figure 9, were drawn with the aid of a camera 

 lucida, using Zeiss 1.5 mm. apochromatic objective, and compensating ocular 12, 

 with tube length of 160 mm. The drawings are reproduced natural size. Figure 

 9 was drawn freehand, but to about the same scale as the others. For the prepara- 

 tion of figures 6, 9, 17, 23 and 24 I am greatly indebted to Miss Mabel L. Hedge. 

 Figures designated as 'oogonial' may be, in some cases, from ovarian follicle 

 cells; the two cannot always be distinguished. 

 1-7 Chromosome groups of Type I. 



1 Drosophila amoena, oogonial metaphase ; from a section (one m-chromosome 

 concealed). 



2 and 3 D. amoena; spermatogonia! metaphases; aceto-carmine. 

 4 and 5 D. ampelophila; oogonial metaphases; aceto-carmine. 



6 D. amoena; second spermatocyte anaphase; side view; showing haploid 

 number of chromosomes; section. 



7 D. quinaria; one pole of anaphase; oogonial division. Polar view showing 

 contrast between large autosomes and sex-chromosomes; ?«-chromosomes not 

 shown; section. 



8 to 13 Groups of Type II. 



8 D. repleta ; oogonial metaphase ; section. 



9 D. repleta; oogonial metaphase slightly earlier than figure 8, showing con- 

 jugation of chromosomes; aceto-carmine. 



10 D. (Species A) ; oogonial metaphase; section. 



11 D. (Species B) ; early metaphase or late prophase; section. 



12 and 13 Same; later stage; sections. 

 14 to 17 Type III. 



14 and 15 D. funebris; metaphase from ovarian cells ;^sections. 



16 D. funebris; earlier than last, showing conjugation of autosomes; section. 



17 D. funebris; anaphase, polar view showing both poles; All chromosomes 

 rod-like; the autosomes completely divided and daughter halves separated; the 

 sex-chromosomes just pulling apart, but still attached at one end; section. 



18 to 20 Type IV. 



18 and 19 D. (Species C); oogonial metaphase; aceto-carmine. 



20 Same; second spermatocyte metaphase; chromosomes partly divided; 

 section. 



21 to 26 TypeV. ■ 



21 D. tripunctata; polar view of metaphase from ovarian cell; section. 



22 D. tripunctata; diagonal view of metaphase; slightly later stage; section. 



23 D. tripunctata; late prophase from ovarian cell; section; h, sex-chromo- 

 somes. 



24 D. tripunctata; early prophase from ovarian cell; autosomes conjugated in 

 pairs; section. 



25 and 26 D. tripunctata; two poles of anaphase from ovarian cell. ShowV- 

 shaped large autosomes (l), rod-like small autosomes (s), and rod-like sex-chro- 

 mosomes (h), section. 



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