Evolutioji a?id Taxonomy 



55 



Fig. 5. — Xenoneura anti- 

 quorum. 



its structure. And the insect described by Moberg {Proiod- 

 mex sihiriais) is supposed by him to be hemipterous, an even 

 more highly specialized type. 



Of devonian insects we know several. Those which are 

 best preserved are Homothetiis fossilis (Fig. 4), XeJioneura anti- 

 quor7ini(yV\<g. 5), zwA Platephemera 

 a7itiqiia (Fig. 6). These differ 

 among themselves to .such an ex- 

 tent that we are forced to conclude 

 without taking into account the 

 two known silurian insects, that 

 already at that earl 5^ time there 

 was a large and varied insect fauna, of which the more 

 primitive forms have not been discovered. 



From the carboniferous rocks much more abundant material 

 has been obtained. But, according to the views of Mr. Scudder 

 "there existed among these ancient forms no ordinal distinc- 

 tions, such as obtain to-day, but they formed a single homo- 

 geneous group of generalized hexapods, which should be 

 separated from later types more by the lack of those special 

 characteristics which are the property of existing orders than 

 by any definite peculiarity of its own. ' ' * 



To this group of generalized 

 hexapods which includes all pa- 

 leozoic insects the name Palceo- 

 didyoptera has been applied. 



Among the Palaeodictyoptera 

 were insects which were un- 

 doubtedly the precursors of the 

 cockroaches, the may-flies, and 

 the walking-sticks. Still these 

 groups of insects " were more closely related to one another, 

 at least in the structure of their wings (which is the only 

 point of general .structure yet open for comparison) than any 

 one of them is to that modern group to which it is most 

 allied." The ordinal distinctions which is now found in 

 the "wing structure of modern insects did not exist in 



Fig. 6. — Platephemera 

 antiqua. 



*Bull. U. S. Geol. Survey. No. 31 p. 104. 



