94 Proceedings of Boyal Society of Edinburgh. [sess. 
It is of course evident, to be quite fair, that in their general 
proposition that the germ was a potential organism, the preforma- 
tionists were quite correct. Their theory was metaphysical, but 
it was at least an advance on the more archaic theological theory 
of possession by spirits. The objection of to-day is simply that a 
model, in the strict sense of the term, does not exist in the germ. 
The early researches of Wolff alone were quite sufficient to show 
that neither the hypothesis of preformation nor its consequent 
hypothesis of “ emboitement” had any basis of fact. From this 
point, therefore, a new start was made. 
2. Special Pangenetic Theories . — Passing from the mystical 
hypotheses, we come to a whole series of theories, which are in 
varying degrees scientific, and may be fairly enough described 
by the general designation pangenetic. They all have this in 
common that they seek to explain the uniqueness of the germ-cell 
by regarding it as a centre of contributions from different parts of 
the organism. 
Early Fwms . — I shall briefly pass over the earlier and vaguer 
forms of this supposition. At such different epochs as are suggested 
by the names of Democritus and Hippocrates, Paracelsus and 
Maupertius, incipient theories of pangenesis — prophecies of Darwin’s 
— were suggested. Thus Democritus maintained that the “ seed ” 
of animals was elaborated by contributions from all parts of the 
body, and that the constituent parts reproduced their several 
origins. Two millennia later Buffon, of whose speculation Darwin 
appears at first to have been unaware, again regards the germs 
as mingled extracts from all parts of the body, or as collections 
of samples from the various organs. If such were indeed the case, 
Buffon and his predecessors saw no further difficulty, for each con- 
tributed sample produced in the embryo a structure like its parental 
origin. 
Spencer’s Theory . — In 1864, in his Principles of Biology, Herbert 
Spencer suggested the existence of “ physiological units,” derived 
from and capable of development into cells, 1 and supposed their 
accumulation in the reproductive elements, which thus become, in 
some conceivable sense, micro-organisms. 
Darwin’s Theory of Pangenesis . — The best known theory of this 
class is, of course, the “ provisional hypothesis of pangenesis” sug- 
