4 THE GENESIS OF THE TERMINOLOGY 



all orders of winged insects, is really the starting point in the actual solution 

 of the problem. 



Before referring farther to Redtenbacher's work, it is desirable to discuss 

 briefly some publications that had a profound influence on it. These treat 

 of the relation of the tracheation of the wings to the wing-venation and of 

 the supposed existence of two morphologically distinct types of wing-veins, 

 the convex and the concave. 



The earliest reference that I have found to the relation of the trachea- 

 tion of the wings to the wing- venation is that of Carl Semper ('57) who 

 stated that in the development of the wing the direction and course of the 

 wing-veins are determined by the tracheas the principal branches of which 

 indicate the wing-veins when of the latter no trace is to be seen. 



Semper, however, did not obtain a correct understanding of the method 

 of development of the wing-veins. He represented a cylinder of epithelial 

 cells, which he states secrete later on their inner surface the chitin that 

 forms the vein. It is evident that he considered the wing-vein as a separate 

 structure from the membrane of the wing. It is an interesting fact that 

 Semper represented a nerve within the wing- vein. Such nerves are now 

 well-known and the connection of their branches with scales and setae 

 has been figured by several writers. 



Landois ('71) figures the larval wings of a Vmiessa and calls atten- 

 tion to the now well-known fact that the larval tracheoles of the wing, the 

 "geknauelten Tracheen," occupy exactly the position occupied later by the 

 wing-veins. He also describes the degeneration of these tracheoles and 

 the development of the permanent tracheae in the same position. He 

 overlooked the fact that the permanent trachese are developed during the 

 last larval stadium, observing them first in the pupal instar. 



A more serious error on the part of Landois was the description of 

 elastic cords covered with an epithelium and closely parallel with the 

 permanent tracheas, in the pupal wing. These he termed the "Fliigel- 

 rippen" and states that they lie close upon the lower membrane of the wing. 

 According to his view a completed wing-vein consists of one of these 

 "Fliigelrippen sensu strictiori," tracheae, and the united upper and lower 

 membranes of the wing enclosing these parts and a space in which the 

 blood flows. 



I can not imagine what Landois saw and described as the "Fliigel- 

 rippen sensu strictiori." I have been unable to find any such structure 

 in any of the wings that I have studied. Spuler ('92) however, gives a figure 

 of a cross-section of a wing-vein in which he represents it, and refers to it 

 in his text as the so-called "Ri])pe" of Semper, but gives no description of it. 



In 1879 the "Ueber Insectenflugel" by G. Ernst Adolph appeared. The 

 publication of this work was unfortunate ; for it added little of value to our 



