Page:The Zoologist, 4th series, vol 3 (1899).djvu/323

Rh Phasmidæ almost prove the pre-existence of the Permian reptiles and the Jurassic birds. If these stick-insects really possessed, and did not derive their imitative structure for protective purposes, then the whole theory of "Protective Resemblance" among insects may go to the wall. The need of protection must undoubtedly have existed in Carboniferous times, if this hypothesis is to stand, and such a view helps to prove, as Huxley has already urged, a pre-Permian existence for reptiles, and, we may add, a greater antiquity also for birds, both of which, we may presume, were, as now, great enemies to insect-life.

The only other explanation—known to the writer—which has been offered to account for the peculiar structure of these Stick-insects, is one proposed by the late Prof. Karl Semper, which would have received additional emphasis had that naturalist been aware (he at least does not allude to the fact) of the Phasma being found as a Carboniferous fossil. Prof. Semper's proposition is that the structure denotes what has been styled "'Larva-forms,' a name given to all animals which possess the characters of the larvæ of other species, and are nevertheless capable of sexual reproduction." The opinion is amplified by the following explanatory illustration:—"Thus species of the same genera, perhaps even the very same species, in our damp and cold climate, do not produce a new generation till they are fully grown; while in the dry warm region of the Mediterranean they have produced two generations before they are fully grown." This would be somewhat on a line with the suggestion we have made that most unicolorous animals are survivals from an original assimilative colouration, and have thus survived by being in