204 Edmund B. Wilson 



EXPLANATION OF PLATE I. 



The figures are reproduced directly from the original photographs, without retouching, at an enlarge- 

 ment of 1500 diameters. It should be borne in mind that in the photographs considerable apparent size- 

 variations are produced by differences of focus, and that unless the chromosomes lie exactly in one plane 

 the photograph often gives a less accurate impression than a drawing. Drawings of most of these photo- 

 graphs with designations, will be found among the text figures, as indicated. 



1 M. terminalis (No. 3, Montogmery's material), 21-chromosome form, first spermatocyte-division 

 polar view; unpaired idiochromosome (odd or accessory) outside the ring, to the right (Fig. 3, h). 



2 M. terminalis (No. 19), 22-chromosome form, first division, polar view; the two separate idio- 

 chromosomes at the right. (The small idiochromosome, being slightly out of focus, appears too small. 

 Its size is correctly shown in the drawing, Fig. 4, h). 



3 M. terminalis (No. 12), 22-cliromosome form similar view; idiochromosomes in contact 



(Fig.4,/)- 



4 M. terminalis (No. 20), 23-chromosome form, one large supernumerary, view similar to the pre- 

 ceding; idiochromosomes and supernumerary to the right (Fig. i, g). 



5 M. granulous (No. 49), 23-chromosome form, one large supernumerary, which lies inside the 

 ring with the small idiochromosome and m-chromosome (Fig. 7, g). 



6 M. terminalis (No. i), 23-chromosome form, one small supernumerary lying inside the ring 

 with the m-chromosome and one of the large bivalents (Fig. 7, ;'). 



7 M. granulosus (No. 52), 24-chromosome form, two large supernumeraries (Fig. 11,^). 



8 M. femoratus (No. 42), 26-chromosome form, four large supernumeraries (Fig. 2, g). 



9 M. terminalis (No. 36), 26-chromosome form, similar to preceding (Fig. 9, e). 



10 M. femoratus (No. 57), 27-chromosome form, four large supernumeraries and one small (Fig. 



13. h)- 



11 M. femoratus (No. 46), 22-chromosome form, first division in side view, both idiochromosomes 



dividing (Fig. 4, /'). 



12 M. granulosus (No. 47) 22-chromosome form, second division, polar view (Fig. 5, c). 



13 M. femoratus (No. 42), 26-chromobome form; second division, polar view, showing hexad ele- 

 ment near center (Fig. 10, a). 



14 M. terminalis (No. 3, Montgomery's material) 21-chromosome form, second division side view, 

 showing lagging idiochromosome ("accessory chromosome") (Fig. 3, /). 



15 From the same cyst as the last, later stage of second division; idiochromosome entering one pole 



(Fig. 3. g)- 



16 M. femoratus (No. 29), 22-chromosome form, second division metaphase in side view, showing 

 idiochromosome bivalent (Uke Fig. 5, d). 



17 M. granulosus (No. 47), 22-chromosome form, late anaphase of second division, one idiochromo- 

 some entering each pole (Fig. 5, /). 



18 M. femoratus (No. 46), abnormal late anaphase of second division, showing both idiochromo- 

 somes passing to the same pole (Fig. 5, 0). 



19 M. femoratus (No. 29), 22-chromosome form, second division showing initial separation of the 

 idiochromosomes (like Fig. 5, /). 



20 M. granulosus (No. 49), 23-chromosome form, one large supernumerary, second division meta- 

 phase, showing triad element formed by the union of the supernumerary with the idiochromosome- 

 bivalent (hke Fig. 8, /). 



21 M. granulosus (No. 52), 24-chromosome form, two large supernumeraries, second division, show, 

 ing tetrad element consisting of the idiochromosomes and supernumeraries united in a linear series (Fig. 

 II, u). 



