which both upper and lower wings have become elongated in an approach to due proportion."[1] This complicated classification, which expresses the difficulties and intricacies of evolution in every sentence, naturally sometimes fails in the details of its own arrangement, but is sufficient to throw more than grave doubts on the explanation offered by Prof. Semper. The consideration of the present knowledge applicable to these Phasmidæ appears to warrant the following conclusions:—
1. The Walking-stick insects are usually considered by naturalists to be undoubted examples of "Protective Resemblance," due to a process of "Natural Selection."
2. If they are found with a somewhat similar structure in the Carboniferous fauna, they must therefore be the result of a previous course of evolution.[2]
3. Reptiles and birds, well-known insect enemies, are generally considered as posterior to the Carboniferous epoch.
4. But as the Permian reptiles were fully developed as we know them now, they must have had an earlier and less differentiated structure; the same suggestion being applicable to the Jurassic birds.
5. The presence of the imitative Phasmidæ in the Carboniferous epoch implies the existence of enemies, probably reptiles, and possibly a transitional form of bird-life.
Good cause is shown why we should seek in past geological epochs for the earliest traces of protective resemblances and mimicry, for the absence of observed attack in the present time does not disprove a great danger and want of protection in the dim eras of the past. "In studying protective resemblance and mimicry among living animals, the exceedingly common occurrence of these phenomena has often forced upon me the con-
- ↑ "Descriptions of Fifty-two New Species of Phasmidæ" (Trans. Linn. Soc. vol. xxv. p. 323).
- ↑ Our knowledge of pre-Carboniferous insects is limited, but present knowledge goes to prove that a considerable insect-fauna existed in more ancient times. Thus, as Mr. Comstock has observed:—"Of Devonian insects we know several.... These differ among themselves to such an extent that we are forced to conclude, without taking into account the two known Silurian insects, that already at that early time there was a large and varied insect-fauna, of which the more primitive forms have not been discovered" ('Evolution and Taxonomy—The Wilder Quarter-Century Book,' p. 55).
