93 
1888-89.] Mr J. A. Thomson on Theory of Heredity. 
that its multiplication or development will result in a new 
organism. (2) Understanding the uniqueness of the germ-cell as 
distinct from other units in the body, why should its division or de- 
velopment follow the old path 1 (3) Granting the general resemblance 
of offspring to parent, what is the truth in regard to the reappear- 
ance of peculiar characters? In what is the germ-cell peculiar, 
what are the rails which rule its course of development, what 
brings hack idiosyncrasies 1 
III. Theories of the Uniqueness of the Germ-Cells. 
1. Mystical Hypotheses . — The theories of heredity, like so many 
others, exhibit three phases — theological, metaphysical, and more 
or less scientific. We need not discuss the possession of the germs 
by spirits, nor yet the postulates of vires formativse, nisus formativus, 
principle of heredity, Yererbungskraft or Bildungstrieb, but begin 
with the gradual emergence of the theories of heredity into fuller 
scientific daylight. It is necessary, however, to linger for a little 
over the so-called mystical hypotheses of the uniqueness of 
the germ-cells. They only require to be stated. According to 
Haller, Bonnet, and others, the seed, egg, or male element con 
tained an excessively minute micro-organism, a complete though 
miniature model of the adult. This is stimulated out of potential 
life in fertilisation, and with the absorption of nutriment in its 
interstices, unfolds or expands into the adult organism. The 
animalculists found this miniature model in the male element, 
which was nourished by the ovum, while the ovists held that 
the model lay in nuce within the egg, and was, so to speak, 
awakened by the sperm. This hypothesis was further backed 
up by that of “ emboitement,” according to which the germ was 
not only itself a marvellous micro-organism, but contained in ever 
smaller proportions, after the manner of an infinite juggler’s box, 
the miniature models of the generations to follow. The germ 
was thus, as they said, like a bud to be unfolded with every part 
ready made or preformed, and all in perfect transparency. “ Es gibt 
kein Werden,” said Haller, and his preformation theory certainly 
disposed at once of development and of the problems of heredity. 
But, at the same time, the germ was far more than a bud — it had 
imprisoned within it the buds of all its descendants. 
