INSECTS
insects known are roaches, or insects closely related to roaches, there were many other forms besides. Some of these are of particular interest to entomologists because, in some ways, they are more simple in structure than are
Fig. 55. Fossil cockroaches from Upper Carboniferous rocks A, Asemoblatta mazona, found in Illinois, length of wing one inch. (From Handlirsch after Scudder.) B, Phyloblatta carbonaria, found in Germany. (From Handlirsch)
any of the modern insects, and in this respect they apparently stand closer to the hypothetical primitive insects than do any others that we know. And yet, the characters by which these oldest known insects, called the Paleodictyoptera, differ from modern forms are so slight that they would scarcely be noticed by anyone except an entomologist; to the casual observer, the Paleodictyoptera would be just insects. Their chief distinguishing marks are in the pattern of the wing venation, which is more symmetrical than in other winged insects, and, therefore, probably closer to that of the primitive ancestors of all the winged insects. These ancient insects probably did not fold the wings over the back, as do most present-day insects, showing thus another primitive
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