584 ; REPORT—1904. 
separation, but the phenomenon of numerically symmetrical disjunction as a feature 
of so many and such different characters seems scarcely favourable to any close 
analogy with chemical processes, If each special character owed its appearance to 
the handing on of some complex molecule as a part of one chemical system, we 
should expect, among such a diversity of characters and forms of life, to encounter 
some phenomenon of valency, manifested as numerical inequality between members 
of allelomorphic pairs. So far, equivalence is certainly the rule, and where the 
characters are simply paired and no resolution has taken place, this rule appears to 
be universal as regards averages. On the other hand, there are features in the 
distribution of characters after resolution, when the second generation (F,) is poly- 
morphic in a high degree, which are not readily accounted for on any hypothesis 
of simple equivalence ; but none of these cases are as yet satisfactorily investigated. 
It is doubtful whether segregation is rightly represented as the separation of 
two characters, and whether we may not more simply imagine that the distinction 
between the allelomorphic gametes is one of presence or absence of some distin- 
guishing element, De Vries has devoted much attention to this question in its 
bearings on his theory of Pangenesis, holding that cases of both kinds occur, and 
attempting to distinguish them. Indications may certainly be enumerated pointing 
in either direction, but for the present I incline to defer a definite opinion. 
If we may profitably seek in the physical world for some parallel to our 
gametic segregations, we shall, I think, find it more close in mechanical separations, 
such as those which may be effected between fluids which do not freely mix, than 
in any strictly chemical phenomenon. In this way we might roughly imitate 
both the ordinary segregation, which is sensibly perfect, and the curious impurity 
occasionally perceptible even in the most pronounced discontinuities, such as those 
which divide male from female, petal from sepal, albino from coloured, horn from 
hair, and so on. 
Gametic Unions and their Consequences. 
Characters being then distributable among gametes according to regular 
systems, the next question concerns the properties and features presented by the 
zygotes formed by the union of gametes bearing different characters. 
As to this no rule can as yet be formulated. Such a heterozygote may exhibit 
one of the allelomorphic characters in its full intensity (even exceeding it in 
special cases, perhaps in connection with increased vigour), or it may be inter- 
mediate between the two, or it may present some character not recognisable in 
either parent. In the latter case it is often, though not always, reversionary. 
When one character appears in such intensity as to conceal or exclude the other 
it is called dominant, the other being recessive. It may be remarked that 
frequently, but certainly not universally (as has been stated), the phylogenetically 
older character is dominant. A curious instance to the contrary is that of the 
peculiar arrangement of colours seen in a breed of game fowls called Brown- 
breasted, which in combination with the purple face, though certainly a modern 
variation, dominates (most markedly in females) over the Black-breasted type of 
Gallus bankiva. 
In a few cases irregularity of dominance has been observed as an exception. 
The clearest illustration I can offer is that of the extra toe in fowls. Generally 
this is a dominant character, but sometimes, as an exceptional phenomenocn, it 
may be recessive, making subsequent analysis very difficult. The nature of this 
irregularity is unknown. A remarkable instance is that of the blue colour in 
maize seeds (Correns; R. H. Lock). Here the dominance of blue is frequently 
imperfect, or absent, and the figures suggest that some regularity in the phe- 
nomenon may be discovered. 
Mendel is often represented as having enunciated dominance as a general 
proposition, That this statement should still be repeated, even by those who 
realise the importance of his discoveries, is an extraordinary illustration of the 
oblivion that has overwhelmed the work of the experimental breeders. Mendel 
makes the specific statement in regard to certain characters in peas which do 
behave thus, but his proposition is not general. ‘To convict him of such a delusion 
