sudden_, and has remained constant ever since."

This is the only case known to me of a new stage in the development
of a Number-Form being suddenly attained.

DESCRIPTION OF PLATE III.

Plate III. is intended to exhibit some instances of heredity. I have
no less than twenty-two families in which this curious tendency is
hereditary, and there may be many more of which I am still ignorant.
I have found it to extend in at least eight of these beyond the near
degrees of parent and child, and brother and sister. Considering that
the occurrence is so rare as to exist in only about one in every
twenty-five or thirty males, these results are very remarkable, and
their trustworthiness is increased by the fact that the hereditary
tendency is on the whole the strongest in those cases where the
Number-Forms are the most defined and elaborate. I give four
instances in which the hereditary tendency is found, not only in
having a Form at all, but also in some degree in the shape of the
Form.

Figs. 46-49 are those of various members of the Henslow family,
where the brothers, sisters, and some children of a sister have the
peculiarity.

Figs. 53-54 are those of a master of Cheltenham College and his
sister.

Figs. 55-56 are those of a father and son; 57 and 58 belong to the
same family.

Figs. 59-60 are those of a brother and sister.

The lower half of the Plate explains itself. The last figure of all,
Fig. 65, is of interest, because it was drawn for an intelligent
little girl of only 11 years old, after she had been closely
questioned by the father, and it was accompanied by elaborate
coloured illustrations of months and days of the week. I thought
this would be a good test case, so I let the matter drop for two
years, and then begged the father to question the child casually,
and to send me a fresh account. I asked at the same time if any
notes had been kept of the previous letter. Nothing could have come
out more satisfactorily. No notes had been kept; the subject
had passed out of mind, but the imagery remained the same, with some
trifling and very interesting metamorphoses of details.

[Illustration: PLATE III. _Examples of an Hereditary Tendency to see
Number-Forms_, _4 Instances where the Number Forms in same family
are alike_ _3 Instances where the Number-Forms in same family are
unlike_]

DESCRIPTION OF PLATE IV.

I can find room in Plate IV. for only two instances of coloured
Number-Forms, though others