54 



John Henry Comstock 



Fig. 3. — Palceoblattina 

 douvillei. 



We are not entirely without evidence that this is the method 

 of the formation of wing veins. It will be shown later that 

 when the principal stem of one system 

 of veins (media) is obliterated and the 

 branches of this system are forced to 

 derive their supply of air through lat- 

 eral tracheae extending to adjacent 

 systems of veins, these lateral tracheae 

 become enveloped by veins resembling 

 in every respect the principal veins. 

 Similar evidence may be drawn from 

 the study of the development of the 

 humeral veins in the Lasiocampidse. 



Since we are not able to determine the form and function of 

 the organs which were modified into wings, let us endeavor to 

 select the most generalized type of wings preserved to us. We 

 will first see what light Palaeontology throws upon this ques- 

 tion 



Comparatively little is known regarding the primitive in- 

 .sects. But thanks to the labors of Mr. S. H. Scudder, who 

 has been one of the chief workers in this field, what is known 

 has been made easily accessible.^ 



Winged insects appeared very early, probably as early as 

 any land plants ; for Moberg has figured 

 an insect (in the Forhandlingar of the 

 Swedish geological society) from the 

 upper part of the lower silurian ; and 

 Brongniart has figured and described a 

 wing from the middle silurian sandstone 

 of Calvados, France. (Fig. 3). But this 



wing instead of being primitive in form represents a rather 

 highly specialized type, if the figure given correctly represents 



*Zittle. Traite de Paleontologie t. II. 

 Bull. U. S. Geol. Survey No. 31. 

 Bull. U. S. Geol. Survey No. 69. 



Fossil Insects of North America. Vol. I. Pretertiary Insects. 

 Index to the known Fossil Insects of the World, including Myria- 

 pods and Arachnids. Bull. U. S. Geol. Survey No. 71, 



Fig. 4. — Homothetus 

 fossilis. 



