146 



TEXT-BOOK OF ENTOMOLOGY 



u< 



FIG. 160. Origin of the wings and their 



veins. After Landois. 



to a trachea ; c the elongated cells, in which, as seen at B, c, a fine 

 tangled tracheal thread () appears, seen to be magnified at C. The 



cell walls break down, and the 

 threads become those which pass 

 through the centre of the veins. 



The wing-rods. Semper discov- 

 ered in transverse sections of the 

 wings, what he called Fliigelrippen ; 

 one such rib accompanying the 

 trachea in each vein. He did not 

 discover its origin, and his descrip- 

 tion of it is said to be somewhat 

 erroneous. Scliaeffer has recently 

 examined the structure, remarking : 

 " I have surely observed the connection of this cellular tube with 

 the tracheae. It is found in the base of the wing where the lumen 

 of the tracheae is much widened. I only describe 

 the fully formed rib (rif>pe). In a cross-section it 

 forms a usually cylindrical tube which is covered 

 by a very thin chitiuous intima which bears deli- 

 cate twigs (Fig. 161). These twigs are analogous 



to the thickened 

 ridge of the 

 tracheal intima. 



I Can 866 11O 



connection be- 



tween the branches of the differ- 

 ent twigs. Through the ribs 

 (I'ippeii) extend a central cord 

 (c) which shows in longitudi- 

 nal section a clear longitudinal 

 streaking. Semper regarded it 

 as a nerve. But the connection 

 of the tube with the trachea con- 

 tradicts this view. I can only 

 regard the cord as a separation- 

 product of the cells of the walls." 



Other historical elements. - 



T^poo qvp tV.p hi nod IvrmYh rnv 



L - lvm P n > l 



puscles, blood-building masses, 

 and nerves. Scliaeffer states that in the immature pupal wings 

 we find besides the large tracheae, which are more or less branched, 



Fl - lei. Section 



of the "rib " of a vein : 

 o, cord; 6, twig. 

 After Schaetter. 



FIG. 162. -Parts of a vein of the cockroach, 

 showing the nerve () by the side of the trachea 

 (tr); o, blood-corpuscles. After Moseley. 



