276 Proceedings of the Royal Physical Society. 
sets of hereditary qualities or transmitting substances, while 
refusing to accept his negative conclusion that it is nothing 
more. We may recognise two phenomena in fertilisation: 
(1) the mingling of hereditary qualities, and (2) a dynamic 
stimulus brought about by the union of sperm with ovum. 
Even Weismann admits that in fertilisation there is not only 
amphimixis, but the restoring to the ovum a certain quantum 
of nuclear substance, without which development does not 
proceed. Even he, as it seems to us, has to recognise two 
phenomena, one of specific, the other of individual import- 
ance. Although he opposes every suggestion of rejuven- 
escence, he admits that the presence of a certain amount 
of nuclear substance in an ovum is essential, and this (brought 
about normally by fertilisation) must have a dynamic effect, 
as to the physiology of which we are ignorant. 
Weismann points out that “we are saturated with the old 
notion that the egg cannot develop without fertilisation, that 
fertilisation is the same as vitalisation.” “Are we not 
aware that, under certain circumstances, the egg can develop 
without fertilisation?” “No one would have regarded 
fertilisation as the vitalising of the egg if the great 
majority of ova had developed parthenogenetically, or if 
science had first become acquainted with parthenogenesis, 
and, later on, with fertilisation.” The notion is bound up 
with the ancient belief in a vital force. To this forcible 
indictment, it may be answered that if the great majority 
of animals had developed by spontaneous generation, no one 
would have regarded biogenesis as an important fact. We 
have to consider the facts as they are, and certainly par- 
thenogenetic forms are in a very small minority. [Why 
they should be in a minority, and that of restricted range, 
Weismann does indeed seek to explain, as we shall after- 
wards consider.]| Nor do we see that the reference to a 
belief in “vital force” is particularly relevant in this 
discussion. For, without entering upon a time-honoured 
controversy, we fail to see that those who believe that the 
sperm physiologically stimulates the ovum are any nearer 
a superstitious belief in a vital force than those who observe 
