mouthful of food before eating it. One idiot is described as often
using his mouth in aid of his hands, whilst hunting for lice. They are
often filthy in their habits, and have no sense of decency; and several
cases have been published of their bodies being remarkably hairy. (37.
Prof. Laycock sums up the character of brute-like idiots by calling
them theroid; Journal of Mental Science, July 1863. Dr. Scott ( The
Deaf and Dumb, 2nd ed. 1870, p. 10) has often observed the imbecile
smelling their food. See, on this same subject, and on the hairiness of
idiots, Dr. Maudsley, Body and Mind, 1870, pp. 46-51. Pinel has also
given a striking case of hairiness in an idiot.)
REVERSION.
Many of the cases to be here given, might have been introduced under
the last heading. When a structure is arrested in its development, but
still continues growing, until it closely resembles a corresponding
structure in some lower and adult member of the same group, it may in
one sense be considered as a case of reversion. The lower members in a
group give us some idea how the common progenitor was probably
constructed; and it is hardly credible that a complex part, arrested at
an early phase of embryonic development, should go on growing so as
ultimately to perform its proper function, unless it had acquired such
power during some earlier state of existence, when the present
exceptional or arrested structure was normal. The simple brain of a
microcephalous idiot, in as far as it resembles that of an ape, may in
this sense be said to offer a case of reversion. (38. In my 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 I now find (see, for instance, Prof. Preyer, Der Kampf um
das Dasein, 1869, s. 45) that mammae erraticae, occur in other
situations, as on the back, in the armpit, and on the thigh; the mammae
in this latter instance having given so much milk that the child was
thus nourished. The probability that the additional mammae are due to
reversion is thus much weakened; nevertheless, it still seems to me
probable, because two pairs are often found symmetrically on the
breast; and of this I myself have received information in several
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