Page:Popular Science Monthly Volume 68.djvu/253

Rh in any rocks older than the Carboniferous. The single specimen reported from the Silurian of France is at best very unlike a cockroach. Its claim to affinity with the cockroach group was long ago contested by Scudder, and even Brongmart, its discoverer, has since conceded that it can not belong here. Other writers exclude the fossil entirely from the class Insecta. The oldest known species appear to be Archimylacris parallela Scudder and Gerablattina fascigera Scudder, from the Millstone Grit, or Middle Carboniferous. During Coal Measure time cockroaches became extremely abundant, more so than in any later period. They are less numerous in Middle and Upper Permian as well as in Mesozoic and later deposits. Nothing whatever is known of the insect life of the southern hemisphere during either Paleozoic or Mesozoic, and it yet remains to be seen what forms will be brought to light from this part of the world. During the Carboniferous and Permian, cockroaches were widely distributed over Europe and North America. With the uniform climatic conditions of that time it can hardly be doubted that their distribution was as wide at least as that of the tropical plants with which they are so constantly associated.

Among the laws of development operative in bringing about the changes which have occurred in the cockroach family during its long geological history, those the effects of which are most apparent may be summarized under the following headings:

—During the nymph stages of a modern cockroach the venation of the immature wing is not unlike that of the typical Coal Measure adult. The main veins of the wing, which during these early stages are free to the base, later become more or less fused and cross veins appear, thus illustrating the law common to most groups of organisms and known as a recapitulation of ancestral characters.