Mayer. — Wing Scales. 
PLATE 4. 
Figures 18-24, 26, 27, Danais plexippus. Figure 25, Pieris rape. 
Fig. 18. Longitudinal section of pupal wing about four days before emergence. 
Figs. 19-24. Successive stages following amitotic division of the nucleus of forma- 
tive cells after the completion of the scales. 
Fig. 25. Portion of a cross section through the mid-dorsal region of a larva of 
Pieris rape, taken just back of the head, in the place where the 
cuticula splits when moults occur. 
Figs. 26,27 Edge and outer surface views, respectively, of the Grundmembran, 
about a week before emergence. 
