N SECTS
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
B
Fro. 5g. Fossil cockroaches from Upper Carboniferous rocks A, tls«?oalatta ??zona, round in lllinois, length of wing one inch. (From Handlirsch after Scudder.) B, Pkvloalatta car?onaria, round in Germany. (From Handlirsch)
any of the modern insects, and in this respect they ap- parently stand doser to the hypothetical primitive insects than do any others that we know. And yet, the charac- ters by which these oldest known insects, called the Paleodictyoptera, differ from modern forms are so slight that they would scarcdy be noticed by anvone except an entomo]ogist; to the casua] observer, the Paleodic- tyoptera would be just insects. Their chief distinguish- ing 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 ances- tors 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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ROACHES
