96 REPORT OF THE CONFERENCE ON GENETICS. 
belonging to distinct physiological systems, may be of great value to the 
breeder. If in the majority of such cases no infallible prescription can 
yet be given to produce the desired result, Mendelian knowledge often 
indicates the course which is most likely to succeed. I am not straining 
the truth when I say that the right course in numbers of instances is one 
which an operator guided by common-sense alone would have studiously 
avoided. 
But, apart from any specific claim as to the immediate economic 
value of genetic research, let me again take more general ground, and 
without fear of contradiction I will insist on the truth that with a critical 
knowledge of the meaning of “pure-bred”’ and “ reversion’’ a new era 
begins. To confusion and guesswork, knowledge and orderly experiment 
succeed. 
The conclusions I have named and others like them have been arrived 
at by statistical observations of a somewhat arduous kind. An account 
of these technical proceedings scarcely falls within the scope of this 
address. I must, however, dwell for a moment on the fact that the 
processes of segregation which bring about the outward and visible facts 
of heredity are in essence symmetrical processes. It has long been 
known, ever since the beginning of microscopical research, that cell- 
division often appears to be a symmetrical process. We have now learnt 
that this visible symmetry is in the main a true representation of the 
qualitative symmetry by which the qualities or characters are distributed 
among the developing germ-cells. No one can yet declare that plans of 
distribution following some higher order of complexity do not exist ; but 
analysis of the simple cases will keep us employed for many a year, and 
not till the symmetrical phenomena of heredity have been exhaustively 
explored can we contemplate a further expedition into the unknown. Of 
one thing at least we may be sure: that heredity is a regular phenomenon, 
in many of its manifestations simple and amenable to experimental 
methods of research. ‘To have said as much in 1899 would have been 
only to make a pious ejaculation of personal faith. Before our meeting 
in 1902 the change had begun. We could deal with simple cases in- 
volving only two types of individuals. When a family contained on an 
average three of one type to one of another, or equal numbers of both, 
we knew what the fact meant. Now we can deal with much more difficult 
cases. The number of types does not trouble us. We understand the 
ratios 9: 7 and 9:3: 4 and 27:9: 28, with many variations on these 
simpler themes. All these can be shown to be produced by the chance 
combinations of germ-cells or gametes produced by symmetrical divisions. 
But ever in our thoughts the question rings, what are these units that 
bring all this to pass, which in their orderly distributions decide so many 
and perhaps all of the attributes or faculties of each creature before it is 
launched into separate existence? Colour, shape, habit, power of 
resistance to disease, and many another property that might be named, 
have one by one been analysed and shown to be alike in the laws of their 
transmission, owing their excitation or extinction to the presence or 
absence of such units or factors. Upon them the success or failure of 
every living thing depends. How the pack is shuffled and dealt we begin 
to perceive: but what are they—the cards? Wild and inscrutable the 
