It is perfectly true, as Morgan says, that new characters which arise as discontinuous variations--in other words, those kinds of variation which are called mutations--do not add themselves to the line of already existing characters, but 'change the adult characters without as it were passing through and beyond them.' The mutations which Morgan describes in his own experiments on _Drosophila_ illustrate this in every case. In no case is the original organ or character, _e.g._ wings, of the normal Fly first developed and then changed by a gradual continuous process into the new character. It might perhaps be said that this took place in the pupa, but that seems impossible, for the complete wing is not fully developed in the pupa. The same truth is equally apparent in the mutations described in _OEnothera_. It follows, therefore, that none of the evolutionary changes which have produced what are called recapitulations can have been due to changes of that kind which is known as mutation. The abnormalities in Pleuronectidae to which I have referred are of the kind usually regarded as due to arrested development. But closer consideration gives rise to doubt concerning the validity of this explanation. It might be supposed that the attached base of the dorsal fin is unable to extend forward because the eye on the edge of the head is in the way, but if the metamorphosis is arrested, why should the fin grow forward in a free projection? I have described a very abnormal specimen of Turbot in a paper communicated to the Zoological Society of London, [Footnote: _Proc. Zool Soc._, 1907.] and in that paper have discussed other possible explanations of these mutations. In the specimen to which I refer the pigmentation instead of being present on both sides was reversed: the lower side was pigmented from the posterior end to the edge of the operculum (Plate II, fig. 2), while the upper side was unpigmented excepting a scattering of minute black specks and a little pigment on the head (Plate II., fig. 1). [Illustration: PLATE II, Fig. 1 and Fig. 2, Abnormal Specimen Of Turbot]