In fact, the resemblances may, in certain instances, be so deeply submerged that they no longer appear in the adult organism at all and are only in evidence during a transitory phase of the embryological process. In such cases, the embryo or larva exhibits, at a particular stage, traces of a uniformity completely obliterated from the adult form. In short, though frequently presented as a distinct argument, embryological similarity, together with all else of value that can still be salvaged from the wreck of the Müller-Haeckel Law of Embryonic Recapitulation, is, at bottom, identical with the general evolutionary argument from homology. In the latter argument we are directed to look beneath the modified surface of the adult organism for surviving vestiges of the ancestral type. In the former, we are bidden to go deeper still, to the extent, that is, of descending into the very embryological process itself, in order to discover lingering traces of the ancestral likeness, which, though now utterly deleted from the transformed adult, are yet partially persistent in certain embryonic phases. In sectioning a larval specimen of the fly-like termite-guest known as _Termitoxenia Heimi_, Father Wasmann came across a typical exemplification of this embryological atavism. In the adult insect, a pair of oar-like appendages replace the wings characteristic of the _Diptera_ (flies). These appendages are organs of exudation, which elaborate a secretion whereof the termites are very fond, and thereby render their possessors welcome guests in the nests of their hosts. The appendages, therefore, though now undoubtedly inherited characters, are the specific means by which these inquilines are adapted to their peculiar environment and mode of life among the termites. Moreover, the organs in question not only differ from wings functionally, but, in the adult, they bear no structural resemblance whatever to the wings of flies. Nevertheless, on examining his sections of the above-mentioned specimen, Wasmann found a developmental stage of brief duration during which wing veins appeared in the posterior branches of the embryonic appendages. Now, assuming that Wasmann’s technique was faultless, his specimen normal, and his interpretation correct, it is rather difficult to avoid his conclusion that we have here, in this transitory larval phase, the last surviving vestige of ancestral wings now wholly obliterated from the adult type, that, consequently, this wingless termite guest is genetically related to the winged _Diptera_, and that we must see in the appendages aboriginal wings diverted from their primitive function and respecialized for the quite different purpose of serving as organs of exudation, (cf. “Modern Biology,” p. 385.) Indeed, phenomena of this kind seem to admit of no other explanation than the atavistic one. It should be remembered, however, that Wasmann does not appear to have verified the observation in more than one specimen,