order of their size from No. 1, the
smallest, to No. 14, the largest, the actual lengths being laid down
from a base line at a suitable distance below, in this case two inches
below the centre, the mean length of the body of the fourteen specimens
being two inches. The respective lengths of the neck, legs, and toe of
each specimen are then laid down in the same manner at convenient
distances apart for comparison; and we see that their variations bear no
definite relation to those of the body, and not much to those of each
other. With the exception of No. 5, in which all the parts agree in
being large, there is a marked independence of each part, shown by the
lines often curving in opposite directions; which proves that in those
specimens one part is large while the other is small. The actual amount
of the variation is very great, ranging from one-sixth of the mean
length in the neck to considerably more than a fourth in the hind leg,
and this among only fourteen examples which happen to be in a particular
museum.

To prove that this is not an isolated case, Professor Milne Edwards also
gives a table showing the amount of variation in the museum specimens of
six common species of lizards, also taking the head as the standard, so
that the comparative variation of each part to the head is given. In the
accompanying diagram (Fig. 2) the variations are exhibited by means of
lines of varying length. It will be understood that, however much the
specimens varied in _size_, if they had kept the same _proportions_, the
variation line would have been in every case reduced to a point, as in
the neck of L. velox which exhibits no variation. The different
proportions of the variation lines for each species may show a distinct
mode of variation, or may be merely due to the small and differing
number of specimens; for it is certain that whatever amount of variation
occurs among a few specimens will be greatly increased when a much
larger number of specimens are examined. That the amount of variation is
large, may be seen by comparing it with the actual length of the head
(given below the diagram) which was used as a standard in determining
the variation, but which itself seems not to have varied.[19]

_Variation among Birds_.

Coming now to the class of Birds, we find much more copious evidence of
variation. This is due partly to the fact that Ornithology has perhaps a
larger body of devotees than any other branch of natural histor