DEVELOPMENT OF THE TRACHEA AND VEINS- 145 



twigs which pass into the imaginal discs. A single longitudinal 

 trachea grows down into the wing-germ (Fig. 147), this branch aris- 

 ing through simple budding of the large body-trachea passing under 

 the rudiment of the wing. 



Gonin states that before the tracheae reach the wing they divide 

 into a great number of capillary tubes united into bundles and often 

 tangled. This mass 

 of tracheae does 

 not penetrate into 

 the wing-germ by 

 one of its free 

 ends, but spread- 

 ing over about 

 third of the sur- 

 face of the wing, 

 separates into a 

 dozen bundles 

 which spread out 

 fan-like in the in- 

 terior of the wing. 

 (Fig. 159). These 

 ramifications, as 

 seen under the mi- 

 croscope, are very 

 irregular; they 

 form here and 

 there knots and 

 anastomoses. They 

 end abruptly in 

 tufts at a little dis- 

 tance from the 

 edge of the wing. 

 A raised semicir- 

 cular ridge (&) surrounds the base of the wing, and within this the 

 capillaries are formed, while on the other side they are covered by 

 a cellular layer. 



Landois, he says, noticed neither the pedicel of the insertion of the wing (i) 

 nor the ridge (6) . Herold only states that the tracheae pass like roots into the 

 wing. Landois believed that they formed an integral part of it. Dewitz and 

 Pancritius used sections to determine their situation. , 



Fig. 160 will illustrate Landois' views as to the origin of the 

 tracheae and veins. A represents the germ of a hind wing attached 



FIG. 159. Germ of a hind wing detached from its insertion, 

 and examined in glycerine : i, pedicel of insertion to the hypoder- 

 mis ; (r, trachea ; 6, semicircular pad ; e, enveloping membrane ; c, 

 bundle of capillary tracheoles ; the large trachete of the wing not 

 visible ; they follow the course of the bundles of tracheoles. 

 After Gonin. 



