I might have given many other examples, but the above are probably sufficient, and will show that the processes which constitute the life-history of the lowest organized beings very closely resemble the first stages in the development of more advanced groups; that as Allen Thomson has truly observed,[92] “the occurrence of segmentation and the regularity of its phenomena are so constant that we may regard it as one of the best established series of facts in organic nature.” It is true that normal yolk-segmentation is not universal in the animal kingdom; that there are great groups in which the yolk does not divide in this manner,—perhaps owing to some difference in its relation to the germinal vesicle, or perhaps because one of the suppressed stages in embryological development, many examples might be given, not only in zoology, but, as I may state on the authority of Dr. Hooker, in botany also. But, however, this may be, it is surely not uninteresting, nor without significance, to find that changes which constitute the life-history of the lowest creatures for the initial stages even of the highest. Returning, in conclusion, to the immediate subject of this work, I have pointed out that many beetles and other insects are derived from larvæ closely resembling _Campodea_. Since, then, individual insects are certainly in many cases developed from larvæ closely resembling the genus _Campodea_, why should it be regarded as incredible that insects as a group have gone through similar stages? That the ancestors of beetles under the influence of varying external conditions, and in the lapse of geological ages, should have undergone changes which the individual beetle passes through under our own eyes and in the space of a few days, is surely no wild or extravagant hypothesis. Again, other insects come from vermiform larvæ much resembling the genus _Lindia_, and it has been also repeatedly shown that in many particulars the embryo of the more specialized forms resembles the full-grown representatives of lower types. I conclude, therefore, that the Insecta generally are descended from ancestors resembling the existing genus _Campodea_, and that these again have arisen from others belonging to a type represented more or less closely by the existing genus _Lindia_.