Two different types may generally, be distinguished.
One of them constitutes a poor variety, the other a rich one. But this
latter is abundant and the first one is poor in instances of exactly the
same conformation. Therefore the difference only lies in the frequency
of the anomaly, and not in its visible features. In discovering an
instance of any anomaly it is therefore impossible to tell whether it
belongs to a poor or to a rich race. This important question can only be
answered by direct sowing-experiments to determine the degree of
heredity.
Monstrosities are often considered as accidents, and rightfully so, at
least as long as they are considered from a morphological point of view.
Physiology of course excludes all accidentality. And in our present ease
it shows [401] that some internal hereditary quality is present, though
often latent, and that the observed anomalies are to be regarded as
responses of this innate tendency to external conditions. Our two types
differ in the frequency of these responses. Rare in the poor race, they
are numerous in the rich variety. The external conditions being the same
for both, the hereditary factor must be different. The tendency is weak
in the one and strong in the other. In both cases, according to my
experience, it may be weakened or strengthened by selection and by
treatment.
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