nowledge
possessed by their framers, and the use they make of it.

From this point of view teratological metamorphosis of all three kinds
demands as much attention as that which is called normal. We can have no
thorough knowledge of an organ, of an individual which is an aggregate
of organs, or of an aggregate of individuals of whatever degree, unless
we know approximately, at least, what are the limits of each. It is not
possible to trace these limits accurately in the case of natural
science, but the larger our knowledge and the wider our generalisations,
the closer will be our approach to the truth.

The most satisfactory classification of malformations would be one
founded upon the nature of the causes inducing the several changes.
Thus, in all organised beings, there is a process of growth, mere
increase in bulk as it were, and a process of evolution or
metamorphosis, in accordance with which certain parts assume a
different form from the rest, in order the better to fit them for the
performance of different offices. Should growth and development be
uniform and regular, that is in accordance with what is habitual in any
particular species, there is no monstrosity, but if either growth or
development be in any way irregular, malformation results. Hence,
theoretically, the best way of grouping cases of malformation would be
according as they are the consequences of:--1st. Arrest of Growth;
2ndly. Excessive Growth; 3rdly. Arrest of Development; 4thly, of
Excessive or Irregular Development.

In practice, however, there are so many objections to this plan that it
has not been found practicable to carry it out. The inability arises to
a great extent from our ignorance of what should be attributed to arrest
of growth, what to excess of development, and so on. Moreover, a student
with a malformed plant before him must necessarily ascertain in what way
it is malformed before he can understand how it became so, and for this
purpose any scheme that will enable him readily to detect the kind of
monstrosity he is examining, even though it be confessedly artificial
and imperfect will be better than a more philosophical arrangement which
circumstances prevent him from employing.

The plan followed in this volume is a slight modification of that
adopted by Moquin-Tandon, and with several additions. In it the aim is
to place before the student certain salient and easily recognisable
points by reference to which the desired in