Page:Popular Science Monthly Volume 68.djvu/251

Rh Some of the cockroaches of Permian time, however, had folded and plicated hind wings. A not uncommon type from the Kansas Permian is that shown in figure 5. This wing has a fold running through the anal area at (b), on one side of which the veins are longitudinal, while, on the other, they run down towards and end on the line of the fold. The wing in the specimen here illustrated is spread out full width. With other specimens, however, it is seen folded in the resting position, the veins of the two parts showing plainly through the thin membrane. Cross veins in the cockroach hind wing are here seen for the first time. A beginning of plication is also evident in the area between (a) and (b), while between the veins are developing accessory longitudinal veins necessary to support such plications. This wing also gives additional evidence of what had been previously demonstrated—plications, although now common to the hind wings of Orthoptera in general, nevertheless originated independently in several families of the order after they had diverged as distinct lines from the main stock. A similar need among the several families is here met by the development in each of a similar mechanism.

The hind wing of modern cockroaches presents a further development of the structures originating with these early ancestors. The hind wing is made to fit nicely under the front by a longitudinal fold. The wing is strengthened by numerous cross veins, and the anal area is very perfectly plicated. An increased expanse of the anal area is accompanied by a relative reduction in the other areas of the wing, especially the cubital. The folded area has remained flexible, while the more exposed part of the wing has become thicker, more resistant, and brownish in color.

This progressive change in the wing structure is accompanied by the reduction of the ovipositor from the long sword-shaped organ of the Carboniferous cockroach to the specialized organ of recent forms adapted to the purpose of holding and guiding the eggs into the egg case. Other organs of the body, if closely followed, would, doubtless, give evidence of similar progressive change. The organs described are those most readily preserved, hence best known in the fossil condition.

The young of any group of organisms are always of interest. A considerable number of young cockroaches have been found in the fossil condition, occurring often in deposits where the bodies of adults are rarely or never seen. In most cases the parts preserved are not the bodies of the young, but the cast off integument shed by the young cockroach with each successive molt. The body is heavy and transported with difficulty, the soft tissue hastens its decay, or more probably it is gathered up as food by the horde of hungry animals in the water or on land. It is not so with the molt, for it is useless as food, and like the detached wings with which it is always associated, is light