Oiiap. IV. 
MANNER OF DEVELOPMENT. 
125 
quently in ancient tlian in recent crania, especially as 
Canestrini has observed in those exhumed from the 
Drift and belonging to the brachycephalic type. Here 
again he comes to the same conclusion as in the ana- 
logous case of the malar bones. In this and other 
instances presently to be given, the cause of ancient 
races approaching the lower animals in certain cha- 
racters more frequently than do the modern races, 
appears to be that the latter stand at a somewhat greater 
distance in the long line of descent from their early 
semi-human progenitors. 
Various other anomalies in man, more or less analo- 
gous with the foregoing, have been advanced by dif- 
ferent authors 37 as cases of reversion ; but these seem 
not a little doubtful, for we have to descend extremely 
low in the mammalian series before we find such struc- 
tures normally present . 38 
37 A whole series of cases is given by Isid. Geoffroy St.-Hilaire, 
4 Hist, des Anomalies,’ tom. iii. p. 437. 
38 In my i Variation of Animals under Domestication ’ (vol. ii. p. 57) 
I attributed the not very rare cases of supernumerary mammae in 
women to reversion. I was led to this as a 'probable conclusion, by the 
additional mammae being generally placed symmetrically on the breast, 
and more especially from one case, in which a single efficient mamma 
occurred in the inguinal region of a woman, the daughter of another 
woman with supernumerary mammae. But Prof. Preyer ( £ Der Kampf 
um das Dasein,’ 1869, s. 45) states that mammae erraticae have been 
known to occur in other situations, even on the back ; so that the force 
of my argument is greatly weakened or perhaps quite destroyed. 
With much hesitation I, in the same work (vol. ii. p. 12), attributed 
the frequent cases of polydactylism in men to reversion. I was partly 
led to this through Prof. Owen’s statement, that some of the Ichthy- 
opterygia possess more than five digits, and therefore, as I supposed, had 
retained a primordial condition; but after reading Prof. Gegenbaur’s 
paper (‘ Jenaischen Zeitschrift,’ B. v. Heft 3, s. 341), who is the highest 
authority in Europe on such a point, and who disputes Owen’s con- 
clusion, I see that it is extremely doubtful whether supernumera^ 
digits can thus be accounted for. It was the fact that such digits not 
only frequently occur and are strongly inherited, but have the power 
of regrowth after amputation, like the normal digits of the lower verte- 
