i\iai. i.,oo.] Mercer: Development of Wings in Lepidoptera. 



10 



List or Aureviatioxs Used in the Figures. 



/' ■ . . Ijegimiing of the invagination of // 



lumen of trachea. 



EXPL.-VNATION OF PLATE I. 

 Pieris rapcr. 



Fig. I. Wing-bud from cross section of larva one-half hour old. 



Fig. 2. Wing-bud from cross section of larva a little older than the one repre- 

 sented in Figure I. 



Fig- 3- Wing-bud from cross section of larva a little older than represented in 

 the two preceding figures, but in the same stage. 



Fig. 4. Wing-bud from cross section of larva after the first moult (second stage). 



F'g- 5- Wing-bud from cross section of larva after the second moult (third stage). 



Fig. 6. Section of wing-bud three sections ahead of the one represented in 

 Figure 5. 



Fig. 6a. A few cells from a wing-bud of the same stage as represented by 

 Figure 6. 



Fig. 7. Wing-bud in cross section of larva after the third moult (early part of 

 the fourth stage). 



Fig. 8. Wing-bud in cross section of larva a little older than the one represen- 

 ted in Figure 7 (fourth stage). 



Fig. 9. Diagrammatic figure showing the proliferation of the trachea. 



Fig. 10. Longi-section of two mother cells of tracheoles. 



Fig. II. Cross section of four mother cells of tracheoles. 



EXPLANATION OF PLATE IL 

 Pieris rapif. 

 Fig. 12. Wing-bud of the fifih larval stage dissected out for direct observation. 

 Fig. 13. Cross section of wing-bud from the fifth stage. 



Fig. 14. Section of the wing-bud in cross section of larva after the fourth moult 

 (fifth stage). 



Fig. 15. Section of trachea showing the connection of tracheoles (fifth stage). 



