HOW THE WINGS GET OUTSIDE OF THE BODY 135 



"The study of the trachese is closely connected with that of the veins 

 (nervures). It is well to guard against the error of Verson, who mistakes for 

 these last the large tracheal branches of the wing. This confusion is easily 

 explained ; it proves that Verson had, with us, recognized that the secondary 

 system is, in the larva, exempt from all respiratory function. Landois thought 



FIG. 147. Left anterior wing- of a larva 3 days before pupation . The posterior part is rolled up : 

 si, prothoracic stigma ; tr. *'., internal tracheal trunk ; tr. e., tr. e.', external tracheal trunk ; p, cavity 

 of a thoracic leg, with the iinaginal bud b. After Gonin. 



that the pupal period was the time of formation of the veins. It seems to me 

 probable that they are derived from the sheath of the peritracheal spaces." 

 (Gonin, pp. 30-33.) 



The appearance of the wing-germs in the fully grown caterpillar, 

 as revealed by simple dissection, is shown at Fig. 146; Fig. 147 



