Pratt. — Imaginal discs. 
PLATE 3. 
Fig. 17. Surface view, dorsal aspect, of the head-fold of an embryo, showing 
the first appearance of the cephalic imaginal discs, x 100. 
Fig. 18. Cross-section through the stomodeum of an embryo somewhat older 
than that represented in Fig. 17. X 130. 
Fig. 19. Cross-section of the same embryo as that shown in Fig. 18, taken at 
some distance further back, showing the cephalic discs where they are 
deepest. X 130. 
Fig. 20. Cross-section through the middle of the same embryo. X 130. 
Fig. 21. Cross-section through the proctodeum of the same embryo. X 130. 
Fig. 22. A somewhat oblique, but nearly sagittal, section of an embryo, the 
stomodeum of which has reached a terminal position. X 130. 
