PLATE 19 



EXPLANATION OF FIGURES 



(S. acuticornis) 



153 A first spermatocyte in prophase. Stage i. Chromosome 11 about to 

 form a ring with a pair of knobs at each end. Near the knobs (x, x) the four parts 

 of the chromosomes are easily distinguishable. 



154 Five stages in the exconjugation of chromosome pair no. 4: a, the 

 members are in parasynapsis ; b, separation of the members has begun, and a 

 second split, at right angles to the first, is now evident; c, separation almost com- 

 plete; e, lateral view of same. 



155a, 155b Nucleus of later prophase, stage j; drawings of two successive 

 sections. All the chromosomes (complete) contained in the two sections. Nos. 

 1 and 2, crosses; 3, a rod probably; 7 and 8, wide V's with knobs at their apices; 

 4, 5, 6, 9, rings; 10, a four-knobbed ring; 11, a double ring. 



156a to 156f Stage j. Showing the primary (first maturation division) 

 split (/, 7), and the secondary (second maturation division) split (77, 77) in 

 various first spermatocyte chromosomes. The proximal exconjugating portions 

 of each pair are indicated by x, x. 



157 Stage k. First spermatocyte in inetaphase; slightly oblique polar view; 

 chromosomes in outline. Nos. 1 to 3 rod-shaped tetrads similar to figures 156a 

 and 156b, and possibly to no. 3 in figure 155b. No. 4 is a cross, like no. 1, figure 

 155b, or no. 2, figure 155a. Nos. 5, 9 are rings similar to 4 or 5, figure 155. Nos. 

 6, 7, 8, 10 are knobbed V's, like nos. 7, 8, figure 155, or figure 156c, or nos. 6, 8, 

 figure 150. No. 11 is a ring resembling figure 152a, or no. 11, figures 150, 151, 

 or 153, or nos. 6, 9, figures 155, 156a. 



316 



