666 TRANSACTIONS OF SECTION K. 
but by indirect methods. For so long as the physical nature of living substance 
remains unknown we can scarcely hope to resolve an individual into its physical 
components. All that can be done is to make comparative analyses of indi- 
viduals and to discover how their several components differ from one another. 
For our present purpose we may represent the individual by an equation :— 
Individual = 2 + ¢; 
where c represents the sum of a long series of characters of the individual and 
a2 an imaginary or real individual groundwork left after all the Mendelian 
characters—the sum of which is c—have been removed by analysis from the 
individual. The Mendelian method is concerned directly with the resolution of 
¢ into its components. Indirectly it is concerned also with x; for by the pursuit 
of the method the full value of c may be determined, and hence that of x may be 
inferred. This concession made, it is permissible to concentrate our attention on 
the term c. 
Thus the business of the Mendelian is to resolve the complex of characters 
which is possessed by an individual into its constituent unit characters. As a 
consequence of this experimental analysis Mendelism is enabled to restate the 
problem of the behaviour in inheritance of two individuals in these terms :— 
The complex of characteristics which distinguishes an individual is the expres- 
sion of the sum of a long series of characters. As the individual arises from 
germ cells so each character arises from a germ within the germ cells. Such 
germs of characters are called factors. When two germ cells unite to form an 
incipient individual or zygote they bring together the similar factors of a given 
character—one factor from the one germ cell and the other from the other. As 
the zygote forms the mature individual, so the paired factors give rise to a 
character of the individual. 
The body characters are the flowers of the factorial seeds implanted in the 
germ cells. 
Some characters are simple and derive from one pair of factors only; others 
are of an ascending order of complexity and may be traced to the co-operative 
agency of two, or more than two, pairs of factors. In the case of a complex 
character the determining factors may be unlike one another or they may be 
alike. Thus two pairs of different factors are required to produce the character 
of colour in certain flowers; on the other hand, it is at least probable that certain 
characters are the outcome of repeated doses of the same factorial stimulant. 
Further, the individual is a dual thing—a double-barrelled gun. Each barrel is 
loaded with the factorial charge supplied by one of the two gametes by whose 
union its duality is constituted. Conversely and consequently a gamete or germ 
cell is, in comparison with the individual, of single and not of dual nature. It has 
one barrel only, and therefore can carry or give effect to one, and only one, of the 
two factorial charges with which the individual was supplied at the time of its 
formation. 
Our image of the double-barrelled gun serves also to illustrate the several 
states in which an individual may find itself with respect to its charge of factors 
of any given simple body character. 
Both barrels of the gun may be loaded. An individual in like state possesses 
two factorial charges and produces gametes all of which are alike in the posses- 
sion of one of these factors. Therefore, such an individual when self-fertilised, 
or mated with its like, produces gametes which are all alike in this respect, and 
these gametes, fusing in pairs, give rise to individuals which all possess the char- 
acter in question. Such individuals are homozygous, they breed true to the 
character. 
Neither barrel may be loaded; and an individual in like state is also 
homozygous. It breeds true to the absence of the character. If a gamete 
of the former individual meet with one from the latter individual, the resulting 
zygote is in like case with that of a double-barrelled gun of which one chamber 
only is loaded. The zygote is heterozygous for the character. Unlike the 
homozygotes, which breed true, the heterozygous individual does not breed true 
to the character in question. 
By the application of the foregoing propositions and a little arithmetic, it 
may be predicted that the offspring of the heterozygote fall into three groups— 
